diff --git a/.gitattributes b/.gitattributes
index f95a950f7..602c23776 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,4 +1,5 @@
-/tests export-ignore
+/.github/ export-ignore
+/tests/ export-ignore
 /.gitattributes export-ignore
 /.gitignore export-ignore
 /.php_cs.dist export-ignore
diff --git a/.github/dependabot.yml b/.github/dependabot.yml
new file mode 100644
index 000000000..0515d2344
--- /dev/null
+++ b/.github/dependabot.yml
@@ -0,0 +1,15 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+  - package-ecosystem: "composer"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+  - package-ecosystem: "github-actions" # See documentation for possible values
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "monthly"
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 000000000..3d665e841
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,63 @@
+name: continuous-integration
+on:
+  push:
+    branches:
+      - master
+      - release/*
+  pull_request:
+jobs:
+  unit-testing:
+    name: PHPUnit (PHP ${{ matrix.php-versions }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        php-versions: ['7.4', '8.0', '8.1', '8.2', '8.3']
+        coverage: ['pcov']
+        code-analysis: ['no']
+        include:
+          - php-versions: '7.4'
+            coverage: 'none'
+            code-analysis: 'yes'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup PHP, with composer and extensions
+        uses: shivammathur/setup-php@v2 #https://github.com/shivammathur/setup-php
+        with:
+          php-version: ${{ matrix.php-versions }}
+          extensions: mbstring, dom, fileinfo, mysql, redis, opcache
+          coverage: ${{ matrix.coverage }}
+          tools: composer
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
+
+      - name: Cache composer dependencies
+        uses: actions/cache@v3
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          # Use composer.json for key, if composer.lock is not committed.
+          # key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.json') }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.json') }}
+          restore-keys: ${{ runner.os }}-composer-
+
+      - name: Install composer dependencies
+        run: composer install --no-progress --prefer-dist --optimize-autoloader
+
+      - name: Code Analysis (PHP CS-Fixer)
+        if: matrix.code-analysis == 'yes'
+        run: php vendor/bin/php-cs-fixer fix --dry-run --diff
+
+      - name: Code Analysis (PHPStan)
+        if: matrix.code-analysis == 'yes'
+        run: composer phpstan
+
+      - name: Test with phpunit
+        run: vendor/bin/phpunit --configuration tests/phpunit.xml --coverage-clover clover.xml
+
+      - name: Code Coverage
+        uses: codecov/codecov-action@v3
+        if: matrix.coverage != 'none'
diff --git a/.gitignore b/.gitignore
index 82b7dad3f..d6e0a1d04 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,4 +6,4 @@ tests/temp
 tests/.phpunit.result.cache
 
 # Development stuff
-.php_cs.cache
+.php-cs-fixer.cache
diff --git a/.php-cs-fixer.dist.php b/.php-cs-fixer.dist.php
new file mode 100644
index 000000000..e981862b7
--- /dev/null
+++ b/.php-cs-fixer.dist.php
@@ -0,0 +1,15 @@
+<?php
+
+$config = new PhpCsFixer\Config();
+$config->getFinder()
+    ->exclude('vendor')
+    ->in(__DIR__)
+    ->append([
+        __FILE__,
+    ]);
+$config->setRules([
+    '@PSR1' => true,
+    '@Symfony' => true,
+]);
+
+return $config;
diff --git a/.php_cs.dist b/.php_cs.dist
deleted file mode 100644
index 4aaf1d90f..000000000
--- a/.php_cs.dist
+++ /dev/null
@@ -1,12 +0,0 @@
-<?php
-
-$config = PhpCsFixer\Config::create();
-$config->getFinder()
-    ->exclude('vendor')
-    ->in(__DIR__);
-$config->setRules([
-    '@PSR1' => true,
-    '@Symfony' => true
-]);
-
-return $config;
diff --git a/CHANGELOG.md b/CHANGELOG.md
index a14c99ab5..22ca89327 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -153,6 +153,121 @@ ChangeLog
 * #3 Add daily occurrences to nextMonth and NextYear
 * #4 Enhance fast forward speed if no count value has been given
 
+4.5.2 (2023-01-20)
+------------------
+
+* #603: Support sabre/xml v4 (@gharlan)
+
+4.5.1 (2022-10-09)
+------------------
+
+* #597: Remove utf8_encode to easily support PHP 8.2 (@phil-davis)
+
+4.5.0 (2022-08-17)
+------------------
+
+* #579: Update .gitattributes (@cedric-anne)
+* #561: PHP 8.1 deprecated support for null values in its APIs (@mstilkerich)
+* #571: Fully ignore invalid lines (@heiglandreas)
+* #564: Fix infinite loop caused by yearly with bySetPos (@liurxliu)
+* #567: Endless loop problem in RRuleIterator::nextDaily (@KristofferFM)
+* #466: Add support for MEMBER in a VCard (@sash04ek)
+* #559: Handle Vobjects without closing tag (@sash04ek)
+* #582: Fix bug in by year day (@KAYLukas)
+
+4.4.3 (2022-07-15)
+------------------
+
+* #577: Ignore multiple same parameter-values (@heiglandreas)
+
+4.4.2 (2022-06-24)
+------------------
+
+* #565: lowercase mailto:-addresses in getNormalizedValue() (@pk1234)
+* #568: Add NICKNAME fallback for VCards without FNs (@Evengard)
+* #573: Component/select: Before uppercasing $child->group, make sure it isn't null (@algernon)
+* #575: Fix encoding detection on PHP 8.1 (@come-nc)
+
+4.4.1 (2021-12-07)
+------------------
+
+ #557: Fix Iterator method signatures and avoid passing null as separator for implode (PHP 8.1 support) (@come-nc)
+
+4.4.0 (2021-11-15)
+------------------
+
+ #548: Allow easier extension of the timezone guessing (@heiglandreas)
+
+4.3.8 (2021-11-14)
+------------------
+
+* #538: fix EventIterator returns wrong end endTime (@floerke)
+* #541: Reordering of the attendees is not a significant change (@floerke)
+* #543: Reordering of vevent is not a significant change (@floerke)
+
+4.3.7 (2021-11-04)
+------------------
+
+* #551: version bump that was missed in 4.3.6 (@phil-davis)
+
+4.3.6 (2021-11-04)
+------------------
+
+* #544: Fix deprecated usages and return types on PHP 8.1 (@cedric-anne)
+
+4.3.5 (2021-02-12)
+------------------
+
+* #523: Fix setting properties with group assignment (@mstilkerich)
+* #532: Make use of until parameter in nextMonthly function (@jaircuevajunior)
+
+4.3.4 (2021-02-04)
+------------------
+
+* #529: Reassign modified date in yearly rrule (@laoneo)
+* #525: Add .gitattributes to reduce package size (@fezfez)
+
+4.3.3 (2020-11-09)
+------------------
+
+* #519: Remove US/Pacific-New obsolete timezone (@phil-davis)
+
+4.3.2 (2020-10-03)
+------------------
+
+* #513: Added Support for PHP 8.0 (@phil-davis)
+
+4.3.1 (2020-07-13)
+------------------
+
+* #510: Fix an incomplete phpdoc type annotation (@mstilkerich)
+* #505: Refactor unit test code for phpunit9 (@phil-davis)
+* #500: Standardize CI (@phil-davis)
+* #496: CI tooling changes (@JeroenVanOort)
+
+4.3.0 (2020-01-31)
+------------------
+
+* Added support for PHP 7.4, dropped support for PHP 7.0 (@phil-davis)
+* #487: Added phpstan coverage, updated testsuite for phpunit8 (@phil-davis, @JeroenVanOort)
+* #495: refactored maps to use ::class notation (@JeroenVanOort)
+
+4.2.2 (2020-01-14)
+------------------
+
+* #465: Add TZ in iTip REPLY iTip messages
+* #486: Add PHONE-NUMBER value type (used for TEL in vCard 3.0)
+
+4.2.1 (2019-12-18)
+------------------
+
+* #469, #451: fix compat with php 7.4
+* #443: prevent running in indefinite loop
+* #449: Preventing creating a component for a root document
+* #450: Fix parse with option Forgiving with trailing equal
+* #459: fixed typo in VCalendar which resulting in usage of the wrong TimeZone
+* #462: Broker::parseEventForOrganizer copies DTSTAMP from $eventInfo that causes broken scheduling
+
 4.2.0 (2019-02-19)
 ------------------
 
@@ -629,7 +744,7 @@ ChangeLog
 * Updated: Windows timezone mapping to latest version from unicode.org
 * Changed: The timezone maps are now loaded in from external files, in
   lib/Sabre/VObject/timezonedata.
-* Added: Fixing badly encoded URL's from google contacts vcards.
+* Added: Fixing badly encoded URL's from Google contacts vcards.
 * Fixed: Issue #68. Couldn't decode properties ending in a colon.
 * Fixed: Issue #72. RecurrenceIterator should respect timezone in the UNTIL
   clause.
@@ -703,7 +818,7 @@ ChangeLog
 * Added: Utility to convert between 2.1, 3.0 and 4.0 vCards.
 * Added: You can now add() multiple parameters to a property in one call.
 * Added: Parameter::has() for easily checking if a parameter value exists.
-* Added: VCard::preferred() to find a preferred email, phone number, etc for a
+* Added: VCard::preferred() to find a preferred email, phone number, etc. for a
   contact.
 * Changed: All $duration properties are now public.
 * Added: A few validators for iCalendar documents.
@@ -900,7 +1015,7 @@ ChangeLog
 ------------------
 
 * Fixed: Microsoft re-uses their magic numbers for different timezones,
-  specifically id 2 for both Sarajevo and Lisbon). A workaround was added to
+  (specifically id 2 for both Sarajevo and Lisbon). A workaround was added to
   deal with this.
 
 
diff --git a/bin/bench_freebusygenerator.php b/bin/bench_freebusygenerator.php
index 963623d18..891335190 100644
--- a/bin/bench_freebusygenerator.php
+++ b/bin/bench_freebusygenerator.php
@@ -11,7 +11,7 @@
     echo "The process will be repeated 100 times to get accurate stats\n";
     echo "\n";
     echo 'Usage: '.$argv[0]." inputfile.ics\n";
-    exit();
+    exit(1);
 }
 
 list(, $inputFile) = $argv;
diff --git a/bin/bench_manipulatevcard.php b/bin/bench_manipulatevcard.php
index df6d9f23d..96a506907 100644
--- a/bin/bench_manipulatevcard.php
+++ b/bin/bench_manipulatevcard.php
@@ -10,7 +10,7 @@
     echo 'system.';
     echo "\n";
     echo 'Usage: '.$argv[0]." inputfile.vcf\n";
-    exit();
+    exit;
 }
 
 list(, $inputFile) = $argv;
diff --git a/bin/generate_vcards b/bin/generate_vcards
index 4663c3c16..758a4438f 100755
--- a/bin/generate_vcards
+++ b/bin/generate_vcards
@@ -3,8 +3,8 @@
 
 namespace Sabre\VObject;
 
-// This sucks.. we have to try to find the composer autoloader. But chances
-// are, we can't find it this way. So we'll do our bestest
+// This sucks. we have to try to find the composer autoloader. But chances
+// are, we can't find it this way. So we'll do our best.
 $paths = [
     __DIR__ . '/../vendor/autoload.php',  // In case vobject is cloned directly
     __DIR__ . '/../../../autoload.php',   // In case vobject is a composer dependency.
diff --git a/bin/generateicalendardata.php b/bin/generateicalendardata.php
index 019ed9745..a3dd3f24e 100755
--- a/bin/generateicalendardata.php
+++ b/bin/generateicalendardata.php
@@ -18,7 +18,7 @@
 
 HI
     );
-    exit();
+    exit;
 }
 
 $events = 100;
diff --git a/bin/mergeduplicates.php b/bin/mergeduplicates.php
index 31b2c14ab..5e48c3c34 100755
--- a/bin/mergeduplicates.php
+++ b/bin/mergeduplicates.php
@@ -3,8 +3,8 @@
 
 namespace Sabre\VObject;
 
-// This sucks.. we have to try to find the composer autoloader. But chances
-// are, we can't find it this way. So we'll do our bestest
+// This sucks. We have to try to find the composer autoloader. But chances
+// are, we can't find it this way. So we'll do our best.
 $paths = [
     __DIR__.'/../vendor/autoload.php',  // In case vobject is cloned directly
     __DIR__.'/../../../autoload.php',   // In case vobject is a composer dependency.
diff --git a/bin/rrulebench.php b/bin/rrulebench.php
index 69008002e..c8be08d46 100644
--- a/bin/rrulebench.php
+++ b/bin/rrulebench.php
@@ -9,7 +9,7 @@
     echo 'system.';
     echo "\n";
     echo 'Usage: '.$argv[0]." inputfile.ics startdate enddate\n";
-    exit();
+    exit;
 }
 
 list(, $inputFile, $startDate, $endDate) = $argv;
diff --git a/bin/vobject b/bin/vobject
index 2aca7e729..53d48ec73 100755
--- a/bin/vobject
+++ b/bin/vobject
@@ -3,8 +3,8 @@
 
 namespace Sabre\VObject;
 
-// This sucks.. we have to try to find the composer autoloader. But chances
-// are, we can't find it this way. So we'll do our bestest
+// This sucks. We have to try to find the composer autoloader. But chances
+// are, we can't find it this way. So we'll do our best.
 $paths = [
     __DIR__ . '/../vendor/autoload.php',  // In case vobject is cloned directly
     __DIR__ . '/../../../autoload.php',   // In case vobject is a composer dependency.
diff --git a/composer.json b/composer.json
index 5ab1e094d..263f6a166 100644
--- a/composer.json
+++ b/composer.json
@@ -32,15 +32,16 @@
     "homepage" : "http://sabre.io/vobject/",
     "license" : "BSD-3-Clause",
     "require" : {
-        "php"          : "^7.1 || ^8.0",
+        "php"          : "^7.4 || ^8.0",
         "ext-mbstring" : "*",
-        "sabre/xml"    : "^2.1"
+        "ext-json"     : "*",
+        "sabre/xml"    : "^3.0 || ^4.0"
     },
     "require-dev" : {
-        "friendsofphp/php-cs-fixer": "~2.17.1",
-        "phpunit/phpunit" : "^7.5 || ^8.5 || ^9.0",
+        "friendsofphp/php-cs-fixer": "^3.38",
+        "phpunit/phpunit" : "^9.6",
         "phpunit/php-invoker" : "^2.0 || ^3.1",
-        "phpstan/phpstan": "^0.12"
+        "phpstan/phpstan": "^1.10"
     },
     "suggest" : {
         "hoa/bench"       : "If you would like to run the benchmark scripts"
@@ -90,7 +91,7 @@
     },
     "scripts": {
         "phpstan": [
-            "phpstan analyse lib tests"
+            "phpstan analyse lib tests --memory-limit 1G"
         ],
         "cs-fixer": [
             "php-cs-fixer fix"
diff --git a/lib/BirthdayCalendarGenerator.php b/lib/BirthdayCalendarGenerator.php
index fade50e16..49793b0d4 100644
--- a/lib/BirthdayCalendarGenerator.php
+++ b/lib/BirthdayCalendarGenerator.php
@@ -15,31 +15,25 @@ class BirthdayCalendarGenerator
 {
     /**
      * Input objects.
-     *
-     * @var array
      */
-    protected $objects = [];
+    protected array $objects = [];
 
     /**
      * Default year.
      * Used for dates without a year.
      */
-    const DEFAULT_YEAR = 2000;
+    public const DEFAULT_YEAR = 2000;
 
     /**
      * Output format for the SUMMARY.
-     *
-     * @var string
      */
-    protected $format = '%1$s\'s Birthday';
+    protected string $format = '%1$s\'s Birthday';
 
     /**
      * Creates the generator.
      *
      * Check the setTimeRange and setObjects methods for details about the
      * arguments.
-     *
-     * @param mixed $objects
      */
     public function __construct($objects = null)
     {
@@ -53,10 +47,8 @@ public function __construct($objects = null)
      *
      * You must either supply a vCard as a string or as a Component/VCard object.
      * It's also possible to supply an array of strings or objects.
-     *
-     * @param mixed $objects
      */
-    public function setObjects($objects)
+    public function setObjects($objects): void
     {
         if (!is_array($objects)) {
             $objects = [$objects];
@@ -81,20 +73,16 @@ public function setObjects($objects)
 
     /**
      * Sets the output format for the SUMMARY.
-     *
-     * @param string $format
      */
-    public function setFormat($format)
+    public function setFormat(string $format): void
     {
         $this->format = $format;
     }
 
     /**
      * Parses the input data and returns a VCALENDAR.
-     *
-     * @return Component/VCalendar
      */
-    public function getResult()
+    public function getResult(): VCalendar
     {
         $calendar = new VCalendar();
 
@@ -111,7 +99,7 @@ public function getResult()
                 continue;
             }
 
-            // We're always converting to vCard 4.0 so we can rely on the
+            // We're always converting to vCard 4.0, so we can rely on the
             // VCardConverter handling the X-APPLE-OMIT-YEAR property for us.
             $object = $object->convert(Document::VCARD40);
 
diff --git a/lib/Cli.php b/lib/Cli.php
index 816e2cb31..69af6f470 100644
--- a/lib/Cli.php
+++ b/lib/Cli.php
@@ -2,7 +2,9 @@
 
 namespace Sabre\VObject;
 
-use InvalidArgumentException;
+use Sabre\VObject\Parser\Json;
+use Sabre\VObject\Parser\MimeDir;
+use Sabre\VObject\Parser\Parser;
 
 /**
  * This is the CLI interface for sabre-vobject.
@@ -15,45 +17,28 @@ class Cli
 {
     /**
      * No output.
-     *
-     * @var bool
-     */
-    protected $quiet = false;
-
-    /**
-     * Help display.
-     *
-     * @var bool
      */
-    protected $showHelp = false;
+    protected bool $quiet = false;
 
     /**
      * Whether to spit out 'mimedir' or 'json' format.
-     *
-     * @var string
      */
-    protected $format;
+    protected ?string $format = null;
 
     /**
      * JSON pretty print.
-     *
-     * @var bool
      */
-    protected $pretty;
+    protected bool $pretty = false;
 
     /**
      * Source file.
-     *
-     * @var string
      */
-    protected $inputPath;
+    protected string $inputPath;
 
     /**
      * Destination file.
-     *
-     * @var string
      */
-    protected $outputPath;
+    protected string $outputPath;
 
     /**
      * output stream.
@@ -78,24 +63,18 @@ class Cli
 
     /**
      * Input format (one of json or mimedir).
-     *
-     * @var string
      */
-    protected $inputFormat;
+    protected ?string $inputFormat = null;
 
     /**
      * Makes the parser less strict.
-     *
-     * @var bool
      */
-    protected $forgiving = false;
+    protected bool $forgiving = false;
 
     /**
      * Main function.
-     *
-     * @return int
      */
-    public function main(array $argv)
+    public function main(array $argv): int
     {
         // @codeCoverageIgnoreStart
         // We cannot easily test this, so we'll skip it. Pretty basic anyway.
@@ -130,34 +109,31 @@ public function main(array $argv)
                         $this->showHelp();
 
                         return 0;
-                        break;
                     case 'format':
                         switch ($value) {
                             // jcard/jcal documents
                             case 'jcard':
                             case 'jcal':
-                            // specific document versions
+                                // specific document versions
                             case 'vcard21':
                             case 'vcard30':
                             case 'vcard40':
                             case 'icalendar20':
-                            // specific formats
+                                // specific formats
                             case 'json':
                             case 'mimedir':
-                            // icalendar/vcad
+                                // icalendar/vcard
                             case 'icalendar':
                             case 'vcard':
                                 $this->format = $value;
                                 break;
 
                             default:
-                                throw new InvalidArgumentException('Unknown format: '.$value);
+                                throw new \InvalidArgumentException('Unknown format: '.$value);
                         }
                         break;
                     case 'pretty':
-                        if (version_compare(PHP_VERSION, '5.4.0') >= 0) {
-                            $this->pretty = true;
-                        }
+                        $this->pretty = true;
                         break;
                     case 'forgiving':
                         $this->forgiving = true;
@@ -171,7 +147,7 @@ public function main(array $argv)
                                 $this->inputFormat = 'json';
                                 break;
 
-                            // mimedir formats
+                                // mimedir formats
                             case 'mimedir':
                             case 'icalendar':
                             case 'vcard':
@@ -183,11 +159,11 @@ public function main(array $argv)
                                 break;
 
                             default:
-                                throw new InvalidArgumentException('Unknown format: '.$value);
+                                throw new \InvalidArgumentException('Unknown format: '.$value);
                         }
                         break;
                     default:
-                        throw new InvalidArgumentException('Unknown option: '.$name);
+                        throw new \InvalidArgumentException('Unknown option: '.$name);
                 }
             }
 
@@ -198,17 +174,17 @@ public function main(array $argv)
             }
 
             if (1 === count($positional)) {
-                throw new InvalidArgumentException('Inputfile is a required argument');
+                throw new \InvalidArgumentException('Inputfile is a required argument');
             }
 
             if (count($positional) > 3) {
-                throw new InvalidArgumentException('Too many arguments');
+                throw new \InvalidArgumentException('Too many arguments');
             }
 
             if (!in_array($positional[0], ['validate', 'repair', 'convert', 'color'])) {
-                throw new InvalidArgumentException('Unknown command: '.$positional[0]);
+                throw new \InvalidArgumentException('Unknown command: '.$positional[0]);
             }
-        } catch (InvalidArgumentException $e) {
+        } catch (\InvalidArgumentException $e) {
             $this->showHelp();
             $this->log('Error: '.$e->getMessage(), 'red');
 
@@ -218,20 +194,20 @@ public function main(array $argv)
         $command = $positional[0];
 
         $this->inputPath = $positional[1];
-        $this->outputPath = isset($positional[2]) ? $positional[2] : '-';
+        $this->outputPath = $positional[2] ?? '-';
 
         if ('-' !== $this->outputPath) {
             $this->stdout = fopen($this->outputPath, 'w');
         }
 
-        if (!$this->inputFormat) {
+        if (null === $this->inputFormat) {
             if ('.json' === substr($this->inputPath, -5)) {
                 $this->inputFormat = 'json';
             } else {
                 $this->inputFormat = 'mimedir';
             }
         }
-        if (!$this->format) {
+        if (null === $this->format) {
             if ('.json' === substr($this->outputPath, -5)) {
                 $this->format = 'json';
             } else {
@@ -262,7 +238,7 @@ public function main(array $argv)
     /**
      * Shows the help message.
      */
-    protected function showHelp()
+    protected function showHelp(): void
     {
         $this->log('Usage:', 'yellow');
         $this->log('  vobject [options] command [arguments]');
@@ -275,10 +251,7 @@ protected function showHelp()
         $this->log('                vcard30, vcard40, icalendar20, jcal, jcard, json, mimedir.');
         $this->log($this->colorize('green', '  --inputformat ').'If the input format cannot be guessed from the extension, it');
         $this->log('                must be specified here.');
-        // Only PHP 5.4 and up
-        if (version_compare(PHP_VERSION, '5.4.0') >= 0) {
-            $this->log($this->colorize('green', '  --pretty      ').'json pretty-print.');
-        }
+        $this->log($this->colorize('green', '  --pretty      ').'json pretty-print.');
         $this->log('');
         $this->log('Commands:', 'yellow');
         $this->log($this->colorize('green', '  validate').' source_file              Validates a file for correctness.');
@@ -286,7 +259,7 @@ protected function showHelp()
         $this->log($this->colorize('green', '  convert').' source_file [output_file] Converts a file.');
         $this->log($this->colorize('green', '  color').' source_file                 Colorize a file, useful for debugging.');
         $this->log(
-        <<<HELP
+            <<<HELP
 
 If source_file is set as '-', STDIN will be used.
 If output_file is omitted, STDOUT will be used.
@@ -306,10 +279,8 @@ protected function showHelp()
 
     /**
      * Validates a VObject file.
-     *
-     * @return int
      */
-    protected function validate(Component $vObj)
+    protected function validate(Component $vObj): int
     {
         $returnCode = 0;
 
@@ -346,10 +317,8 @@ protected function validate(Component $vObj)
 
     /**
      * Repairs a VObject file.
-     *
-     * @return int
      */
-    protected function repair(Component $vObj)
+    protected function repair(Component $vObj): int
     {
         $returnCode = 0;
 
@@ -387,12 +356,8 @@ protected function repair(Component $vObj)
 
     /**
      * Converts a vObject file to a new format.
-     *
-     * @param Component $vObj
-     *
-     * @return int
      */
-    protected function convert($vObj)
+    protected function convert(Component $vObj): int
     {
         $json = false;
         $convertVersion = null;
@@ -451,22 +416,18 @@ protected function convert($vObj)
 
     /**
      * Colorizes a file.
-     *
-     * @param Component $vObj
      */
-    protected function color($vObj)
+    protected function color(Component $vObj): int
     {
-        fwrite($this->stdout, $this->serializeComponent($vObj));
+        $this->serializeComponent($vObj);
+
+        return 0;
     }
 
     /**
      * Returns an ansi color string for a color name.
-     *
-     * @param string $color
-     *
-     * @return string
      */
-    protected function colorize($color, $str, $resetTo = 'default')
+    protected function colorize(string $color, string $str, string $resetTo = 'default'): string
     {
         $colors = [
             'cyan' => '1;36',
@@ -483,16 +444,13 @@ protected function colorize($color, $str, $resetTo = 'default')
 
     /**
      * Writes out a string in specific color.
-     *
-     * @param string $color
-     * @param string $str
      */
-    protected function cWrite($color, $str)
+    protected function cWrite(string $color, string $str): void
     {
         fwrite($this->stdout, $this->colorize($color, $str));
     }
 
-    protected function serializeComponent(Component $vObj)
+    protected function serializeComponent(Component $vObj): void
     {
         $this->cWrite('cyan', 'BEGIN');
         $this->cWrite('red', ':');
@@ -507,48 +465,40 @@ protected function serializeComponent(Component $vObj)
          * To avoid score collisions, each "score category" has a reasonable
          * space to accommodate elements. The $key is added to the $score to
          * preserve the original relative order of elements.
-         *
-         * @param int   $key
-         * @param array $array
-         *
-         * @return int
          */
-        $sortScore = function ($key, $array) {
+        $sortScore = function (int $key, array $array): int {
             if ($array[$key] instanceof Component) {
                 // We want to encode VTIMEZONE first, this is a personal
                 // preference.
                 if ('VTIMEZONE' === $array[$key]->name) {
                     $score = 300000000;
-
-                    return $score + $key;
                 } else {
                     $score = 400000000;
-
-                    return $score + $key;
                 }
-            } else {
-                // Properties get encoded first
-                // VCARD version 4.0 wants the VERSION property to appear first
-                if ($array[$key] instanceof Property) {
-                    if ('VERSION' === $array[$key]->name) {
-                        $score = 100000000;
-
-                        return $score + $key;
-                    } else {
-                        // All other properties
-                        $score = 200000000;
 
-                        return $score + $key;
-                    }
+                return $score + $key;
+            }
+            // Properties get encoded first
+            // VCARD version 4.0 wants the VERSION property to appear first
+            if ($array[$key] instanceof Property) {
+                if ('VERSION' === $array[$key]->name) {
+                    $score = 100000000;
+                } else {
+                    // All other properties
+                    $score = 200000000;
                 }
+
+                return $score + $key;
             }
+
+            return 0;
         };
 
         $children = $vObj->children();
         $tmp = $children;
         uksort(
             $children,
-            function ($a, $b) use ($sortScore, $tmp) {
+            function ($a, $b) use ($sortScore, $tmp): int {
                 $sA = $sortScore($a, $tmp);
                 $sB = $sortScore($b, $tmp);
 
@@ -572,7 +522,7 @@ function ($a, $b) use ($sortScore, $tmp) {
     /**
      * Colorizes a property.
      */
-    protected function serializeProperty(Property $property)
+    protected function serializeProperty(Property $property): void
     {
         if ($property->group) {
             $this->cWrite('default', $property->group);
@@ -630,7 +580,7 @@ protected function serializeProperty(Property $property)
     /**
      * Parses the list of arguments.
      */
-    protected function parseArguments(array $argv)
+    protected function parseArguments(array $argv): array
     {
         $positional = [];
         $options = [];
@@ -664,14 +614,16 @@ protected function parseArguments(array $argv)
         return [$options, $positional];
     }
 
-    protected $parser;
+    protected ?Parser $parser = null;
 
     /**
      * Reads the input file.
      *
-     * @return Component
+     * @throws EofException
+     * @throws ParseException
+     * @throws InvalidDataException
      */
-    protected function readInput()
+    protected function readInput(): ?Document
     {
         if (!$this->parser) {
             if ('-' !== $this->inputPath) {
@@ -679,9 +631,9 @@ protected function readInput()
             }
 
             if ('mimedir' === $this->inputFormat) {
-                $this->parser = new Parser\MimeDir($this->stdin, ($this->forgiving ? Reader::OPTION_FORGIVING : 0));
+                $this->parser = new MimeDir($this->stdin, $this->forgiving ? Reader::OPTION_FORGIVING : 0);
             } else {
-                $this->parser = new Parser\Json($this->stdin, ($this->forgiving ? Reader::OPTION_FORGIVING : 0));
+                $this->parser = new Json($this->stdin, $this->forgiving ? Reader::OPTION_FORGIVING : 0);
             }
         }
 
@@ -690,10 +642,8 @@ protected function readInput()
 
     /**
      * Sends a message to STDERR.
-     *
-     * @param string $msg
      */
-    protected function log($msg, $color = 'default')
+    protected function log(string $msg, string $color = 'default'): void
     {
         if (!$this->quiet) {
             if ('default' !== $color) {
diff --git a/lib/Component.php b/lib/Component.php
index c1a63258e..426695470 100644
--- a/lib/Component.php
+++ b/lib/Component.php
@@ -2,6 +2,7 @@
 
 namespace Sabre\VObject;
 
+use Sabre\VObject;
 use Sabre\Xml;
 
 /**
@@ -13,6 +14,8 @@
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
+ *
+ * @property VObject\Property\FlatText UID
  */
 class Component extends Node
 {
@@ -20,17 +23,15 @@ class Component extends Node
      * Component name.
      *
      * This will contain a string such as VEVENT, VTODO, VCALENDAR, VCARD.
-     *
-     * @var string
      */
-    public $name;
+    public string $name;
 
     /**
      * A list of properties and/or sub-components.
      *
-     * @var array
+     * @var array<string, Component|Property>
      */
-    protected $children = [];
+    protected array $children = [];
 
     /**
      * Creates a new component.
@@ -43,12 +44,11 @@ class Component extends Node
      * an iCalendar object, this may be something like CALSCALE:GREGORIAN. To
      * ensure that this does not happen, set $defaults to false.
      *
-     * @param string $name     such as VCALENDAR, VEVENT
-     * @param bool   $defaults
+     * @param string|null $name such as VCALENDAR, VEVENT
      */
-    public function __construct(Document $root, $name, array $children = [], $defaults = true)
+    public function __construct(Document $root, ?string $name, array $children = [], bool $defaults = true)
     {
-        $this->name = strtoupper($name);
+        $this->name = isset($name) ? strtoupper($name) : '';
         $this->root = $root;
 
         if ($defaults) {
@@ -97,10 +97,8 @@ public function __construct(Document $root, $name, array $children = [], $defaul
      * add($name, $value, array $parameters = []) // Adds a new property
      * add($name, array $children = []) // Adds a new component
      * by name.
-     *
-     * @return Node
      */
-    public function add()
+    public function add(): Node
     {
         $arguments = func_get_args();
 
@@ -116,6 +114,7 @@ public function add()
             throw new \InvalidArgumentException('The first argument must either be a \\Sabre\\VObject\\Node or a string');
         }
 
+        /** @var Component|Property|Parameter $newNode */
         $name = $newNode->name;
         if (isset($this->children[$name])) {
             $this->children[$name][] = $newNode;
@@ -136,10 +135,10 @@ public function add()
      *
      * @param string|Property|Component $item
      */
-    public function remove($item)
+    public function remove($item): void
     {
         if (is_string($item)) {
-            // If there's no dot in the name, it's an exact property name and
+            // If there's no dot in the name, it's an exact property name,
             // we can just wipe out all those properties.
             //
             if (false === strpos($item, '.')) {
@@ -168,10 +167,8 @@ public function remove($item)
     /**
      * Returns a flat list of all the properties and components in this
      * component.
-     *
-     * @return array
      */
-    public function children()
+    public function children(): array
     {
         $result = [];
         foreach ($this->children as $childGroup) {
@@ -184,10 +181,8 @@ public function children()
     /**
      * This method only returns a list of sub-components. Properties are
      * ignored.
-     *
-     * @return array
      */
-    public function getComponents()
+    public function getComponents(): array
     {
         $result = [];
 
@@ -211,15 +206,11 @@ public function getComponents()
      * search for a property in a specific group, you can select on the entire
      * string ("HOME.EMAIL"). If you want to search on a specific property that
      * has not been assigned a group, specify ".EMAIL".
-     *
-     * @param string|null $name
-     *
-     * @return array
      */
-    public function select($name)
+    public function select(string $name): array
     {
         $group = null;
-        $name = is_null($name) ? '' : strtoupper($name);
+        $name = strtoupper($name);
         if (false !== strpos($name, '.')) {
             list($group, $name) = explode('.', $name, 2);
         }
@@ -228,7 +219,7 @@ public function select($name)
         }
 
         if (!is_null($name)) {
-            $result = isset($this->children[$name]) ? $this->children[$name] : [];
+            $result = $this->children[$name] ?? [];
 
             if (is_null($group)) {
                 return $result;
@@ -238,7 +229,7 @@ public function select($name)
                 return array_filter(
                     $result,
                     function ($child) use ($group) {
-                        return $child instanceof Property && strtoupper($child->group ?? '') === $group;
+                        return $child instanceof Property && (null !== $child->group ? strtoupper($child->group) : '') === $group;
                     }
                 );
             }
@@ -249,7 +240,7 @@ function ($child) use ($group) {
         $result = [];
         foreach ($this->children as $childGroup) {
             foreach ($childGroup as $child) {
-                if ($child instanceof Property && $child->group && strtoupper($child->group) === $group) {
+                if ($child instanceof Property && (null !== $child->group ? strtoupper($child->group) : '') === $group) {
                     $result[] = $child;
                 }
             }
@@ -260,10 +251,8 @@ function ($child) use ($group) {
 
     /**
      * Turns the object back into a serialized blob.
-     *
-     * @return string
      */
-    public function serialize()
+    public function serialize(): string
     {
         $str = 'BEGIN:'.$this->name."\r\n";
 
@@ -282,42 +271,39 @@ public function serialize()
          *
          * @return int
          */
-        $sortScore = function ($key, $array) {
+        $sortScore = function (int $key, array $array): ?int {
             if ($array[$key] instanceof Component) {
                 // We want to encode VTIMEZONE first, this is a personal
                 // preference.
                 if ('VTIMEZONE' === $array[$key]->name) {
                     $score = 300000000;
-
-                    return $score + $key;
                 } else {
                     $score = 400000000;
-
-                    return $score + $key;
                 }
-            } else {
-                // Properties get encoded first
-                // VCARD version 4.0 wants the VERSION property to appear first
-                if ($array[$key] instanceof Property) {
-                    if ('VERSION' === $array[$key]->name) {
-                        $score = 100000000;
-
-                        return $score + $key;
-                    } else {
-                        // All other properties
-                        $score = 200000000;
-
-                        return $score + $key;
-                    }
+
+                return $score + $key;
+            }
+            // Properties get encoded first
+            // VCARD version 4.0 wants the VERSION property to appear first
+            if ($array[$key] instanceof Property) {
+                if ('VERSION' === $array[$key]->name) {
+                    $score = 100000000;
+                } else {
+                    // All other properties
+                    $score = 200000000;
                 }
+
+                return $score + $key;
             }
+
+            return 0;
         };
 
         $children = $this->children();
         $tmp = $children;
         uksort(
             $children,
-            function ($a, $b) use ($sortScore, $tmp) {
+            function ($a, $b) use ($sortScore, $tmp): int {
                 $sA = $sortScore($a, $tmp);
                 $sB = $sortScore($b, $tmp);
 
@@ -336,11 +322,9 @@ function ($a, $b) use ($sortScore, $tmp) {
     /**
      * This method returns an array, with the representation as it should be
      * encoded in JSON. This is used to create jCard or jCal documents.
-     *
-     * @return array
      */
     #[\ReturnTypeWillChange]
-    public function jsonSerialize()
+    public function jsonSerialize(): array
     {
         $components = [];
         $properties = [];
@@ -368,7 +352,7 @@ public function jsonSerialize()
      *
      * @param Xml\Writer $writer XML writer
      */
-    public function xmlSerialize(Xml\Writer $writer)
+    public function xmlSerialize(Xml\Writer $writer): void
     {
         $components = [];
         $properties = [];
@@ -410,10 +394,8 @@ public function xmlSerialize(Xml\Writer $writer)
 
     /**
      * This method should return a list of default property values.
-     *
-     * @return array
      */
-    protected function getDefaults()
+    protected function getDefaults(): array
     {
         return [];
     }
@@ -430,11 +412,9 @@ protected function getDefaults()
      *
      * $event = $calendar->VEVENT;
      *
-     * @param string $name
-     *
-     * @return Property|null
+     * @return Property|Component|null
      */
-    public function __get($name)
+    public function __get(string $name): ?Node
     {
         if ('children' === $name) {
             throw new \RuntimeException('Starting sabre/vobject 4.0 the children property is now protected. You should use the children() method instead');
@@ -442,7 +422,7 @@ public function __get($name)
 
         $matches = $this->select($name);
         if (0 === count($matches)) {
-            return;
+            return null;
         } else {
             $firstMatch = current($matches);
             /* @var $firstMatch Property */
@@ -454,12 +434,8 @@ public function __get($name)
 
     /**
      * This method checks if a sub-element with the specified name exists.
-     *
-     * @param string $name
-     *
-     * @return bool
      */
-    public function __isset($name)
+    public function __isset(string $name): bool
     {
         $matches = $this->select($name);
 
@@ -474,11 +450,8 @@ public function __isset($name)
      *
      * If the item already exists, it will be removed. If you want to add
      * a new item with the same name, always use the add() method.
-     *
-     * @param string $name
-     * @param mixed  $value
      */
-    public function __set($name, $value)
+    public function __set(string $name, $value): void
     {
         $name = strtoupper($name);
         $this->remove($name);
@@ -492,10 +465,8 @@ public function __set($name, $value)
     /**
      * Removes all properties and components within this component with the
      * specified name.
-     *
-     * @param string $name
      */
-    public function __unset($name)
+    public function __unset(string $name): void
     {
         $this->remove($name);
     }
@@ -536,10 +507,8 @@ public function __clone()
      *
      * See the VEVENT implementation for getValidationRules for a more complex
      * example.
-     *
-     * @var array
      */
-    public function getValidationRules()
+    public function getValidationRules(): array
     {
         return [];
     }
@@ -563,12 +532,8 @@ public function getValidationRules()
      *   1 - The issue was repaired (only happens if REPAIR was turned on).
      *   2 - A warning.
      *   3 - An error.
-     *
-     * @param int $options
-     *
-     * @return array
      */
-    public function validate($options = 0)
+    public function validate(int $options = 0): array
     {
         $rules = $this->getValidationRules();
         $defaults = $this->getDefaults();
@@ -659,7 +624,7 @@ public function validate($options = 0)
      * It's intended to remove all circular references, so PHP can easily clean
      * it up.
      */
-    public function destroy()
+    public function destroy(): void
     {
         parent::destroy();
         foreach ($this->children as $childGroup) {
diff --git a/lib/Component/Available.php b/lib/Component/Available.php
index 5510b9e0a..b3ba40b07 100644
--- a/lib/Component/Available.php
+++ b/lib/Component/Available.php
@@ -13,6 +13,10 @@
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
  * @author Ivan Enderlin
  * @license http://sabre.io/license/ Modified BSD License
+ *
+ * @property VObject\Property\ICalendar\DateTime DTSTART
+ * @property VObject\Property\ICalendar\DateTime DTEND
+ * @property VObject\Property\ICalendar\Duration DURATION
  */
 class Available extends VObject\Component
 {
@@ -26,9 +30,9 @@ class Available extends VObject\Component
      * If either the start or end is 'unbounded' its value will be null
      * instead.
      *
-     * @return array
+     * @throws VObject\InvalidDataException
      */
-    public function getEffectiveStartEnd()
+    public function getEffectiveStartEnd(): array
     {
         $effectiveStart = $this->DTSTART->getDateTime();
         if (isset($this->DTEND)) {
@@ -52,10 +56,8 @@ public function getEffectiveStartEnd()
      *   * + - Must appear at least once.
      *   * * - Can appear any number of times.
      *   * ? - May appear, but not more than once.
-     *
-     * @var array
      */
-    public function getValidationRules()
+    public function getValidationRules(): array
     {
         return [
             'UID' => 1,
@@ -101,12 +103,8 @@ public function getValidationRules()
      *   1 - The issue was repaired (only happens if REPAIR was turned on).
      *   2 - A warning.
      *   3 - An error.
-     *
-     * @param int $options
-     *
-     * @return array
      */
-    public function validate($options = 0)
+    public function validate(int $options = 0): array
     {
         $result = parent::validate($options);
 
diff --git a/lib/Component/VAlarm.php b/lib/Component/VAlarm.php
index bd00eb600..3e5797b0a 100644
--- a/lib/Component/VAlarm.php
+++ b/lib/Component/VAlarm.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\Component;
 
-use DateTimeImmutable;
-use DateTimeInterface;
 use Sabre\VObject;
 use Sabre\VObject\InvalidDataException;
 
@@ -15,6 +13,12 @@
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
+ *
+ * @property VObject\Property\ICalendar\DateTime DTSTART
+ * @property VObject\Property\ICalendar\DateTime DTEND
+ * @property VObject\Property\ICalendar\Duration DURATION
+ * @property VObject\Property\ICalendar\Duration|VObject\Property\ICalendar\DateTime TRIGGER
+ * @property VObject\Property\IntegerValue REPEAT
  */
 class VAlarm extends VObject\Component
 {
@@ -23,15 +27,16 @@ class VAlarm extends VObject\Component
      *
      * This ignores repeated alarm, only the first trigger is returned.
      *
-     * @return DateTimeImmutable
+     * @throws InvalidDataException
      */
-    public function getEffectiveTriggerTime()
+    public function getEffectiveTriggerTime(): \DateTimeImmutable
     {
         $trigger = $this->TRIGGER;
-        if (!isset($trigger['VALUE']) || 'DURATION' === strtoupper($trigger['VALUE'])) {
+        if (!isset($trigger['VALUE']) || ($trigger['VALUE'] && 'DURATION' === strtoupper($trigger['VALUE']))) {
             $triggerDuration = VObject\DateTimeParser::parseDuration($this->TRIGGER);
             $related = (isset($trigger['RELATED']) && 'END' == strtoupper($trigger['RELATED'])) ? 'END' : 'START';
 
+            /** @var VEvent|VTodo $parentComponent */
             $parentComponent = $this->parent;
             if ('START' === $related) {
                 if ('VTODO' === $parentComponent->name) {
@@ -41,7 +46,6 @@ public function getEffectiveTriggerTime()
                 }
 
                 $effectiveTrigger = $parentComponent->$propName->getDateTime();
-                $effectiveTrigger = $effectiveTrigger->add($triggerDuration);
             } else {
                 if ('VTODO' === $parentComponent->name) {
                     $endProp = 'DUE';
@@ -53,17 +57,15 @@ public function getEffectiveTriggerTime()
 
                 if (isset($parentComponent->$endProp)) {
                     $effectiveTrigger = $parentComponent->$endProp->getDateTime();
-                    $effectiveTrigger = $effectiveTrigger->add($triggerDuration);
                 } elseif (isset($parentComponent->DURATION)) {
                     $effectiveTrigger = $parentComponent->DTSTART->getDateTime();
                     $duration = VObject\DateTimeParser::parseDuration($parentComponent->DURATION);
                     $effectiveTrigger = $effectiveTrigger->add($duration);
-                    $effectiveTrigger = $effectiveTrigger->add($triggerDuration);
                 } else {
                     $effectiveTrigger = $parentComponent->DTSTART->getDateTime();
-                    $effectiveTrigger = $effectiveTrigger->add($triggerDuration);
                 }
             }
+            $effectiveTrigger = $effectiveTrigger->add($triggerDuration);
         } else {
             $effectiveTrigger = $trigger->getDateTime();
         }
@@ -78,12 +80,9 @@ public function getEffectiveTriggerTime()
      * The rules used to determine if an event falls within the specified
      * time-range is based on the CalDAV specification.
      *
-     * @param DateTime $start
-     * @param DateTime $end
-     *
-     * @return bool
+     * @throws InvalidDataException
      */
-    public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
+    public function isInTimeRange(\DateTimeInterface $start, \DateTimeInterface $end): bool
     {
         $effectiveTrigger = $this->getEffectiveTriggerTime();
 
@@ -120,10 +119,8 @@ public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
      *   * + - Must appear at least once.
      *   * * - Can appear any number of times.
      *   * ? - May appear, but not more than once.
-     *
-     * @var array
      */
-    public function getValidationRules()
+    public function getValidationRules(): array
     {
         return [
             'ACTION' => 1,
diff --git a/lib/Component/VAvailability.php b/lib/Component/VAvailability.php
index 04ec38dcb..ff6e9bd65 100644
--- a/lib/Component/VAvailability.php
+++ b/lib/Component/VAvailability.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Component;
 
-use DateTimeInterface;
 use Sabre\VObject;
 
 /**
@@ -14,6 +13,10 @@
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
  * @author Ivan Enderlin
  * @license http://sabre.io/license/ Modified BSD License
+ *
+ * @property VObject\Property\ICalendar\DateTime DTSTART
+ * @property VObject\Property\ICalendar\DateTime DTEND
+ * @property VObject\Property\ICalendar\Duration DURATION
  */
 class VAvailability extends VObject\Component
 {
@@ -26,15 +29,15 @@ class VAvailability extends VObject\Component
      *
      * https://tools.ietf.org/html/draft-daboo-calendar-availability-05#section-3.1
      *
-     * @return bool
+     * @throws VObject\InvalidDataException
      */
-    public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
+    public function isInTimeRange(\DateTimeInterface $start, \DateTimeInterface $end): bool
     {
         list($effectiveStart, $effectiveEnd) = $this->getEffectiveStartEnd();
 
         return
-            (is_null($effectiveStart) || $start < $effectiveEnd) &&
-            (is_null($effectiveEnd) || $end > $effectiveStart)
+            (is_null($effectiveStart) || $start < $effectiveEnd)
+            && (is_null($effectiveEnd) || $end > $effectiveStart)
         ;
     }
 
@@ -48,9 +51,9 @@ public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
      * If either the start or end is 'unbounded' its value will be null
      * instead.
      *
-     * @return array
+     * @throws VObject\InvalidDataException
      */
-    public function getEffectiveStartEnd()
+    public function getEffectiveStartEnd(): array
     {
         $effectiveStart = null;
         $effectiveEnd = null;
@@ -79,10 +82,8 @@ public function getEffectiveStartEnd()
      *   * + - Must appear at least once.
      *   * * - Can appear any number of times.
      *   * ? - May appear, but not more than once.
-     *
-     * @var array
      */
-    public function getValidationRules()
+    public function getValidationRules(): array
     {
         return [
             'UID' => 1,
@@ -127,12 +128,8 @@ public function getValidationRules()
      *   1 - The issue was repaired (only happens if REPAIR was turned on).
      *   2 - A warning.
      *   3 - An error.
-     *
-     * @param int $options
-     *
-     * @return array
      */
-    public function validate($options = 0)
+    public function validate(int $options = 0): array
     {
         $result = parent::validate($options);
 
diff --git a/lib/Component/VCalendar.php b/lib/Component/VCalendar.php
index 4db318135..b317e02c8 100644
--- a/lib/Component/VCalendar.php
+++ b/lib/Component/VCalendar.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\Component;
 
-use DateTimeInterface;
-use DateTimeZone;
 use Sabre\VObject;
 use Sabre\VObject\Component;
 use Sabre\VObject\InvalidDataException;
@@ -19,6 +17,11 @@
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
+ *
+ * @property VEvent VEVENT
+ * @property VJournal VJOURNAL
+ * @property VObject\Property\Text ORG
+ * @property VObject\Property\FlatText METHOD
  */
 class VCalendar extends VObject\Document
 {
@@ -26,17 +29,13 @@ class VCalendar extends VObject\Document
      * The default name for this component.
      *
      * This should be 'VCALENDAR' or 'VCARD'.
-     *
-     * @var string
      */
-    public static $defaultName = 'VCALENDAR';
+    public static ?string $defaultName = 'VCALENDAR';
 
     /**
      * This is a list of components, and which classes they should map to.
-     *
-     * @var array
      */
-    public static $componentMap = [
+    public static array $componentMap = [
         'VCALENDAR' => self::class,
         'VALARM' => VAlarm::class,
         'VEVENT' => VEvent::class,
@@ -50,10 +49,8 @@ class VCalendar extends VObject\Document
 
     /**
      * List of value-types, and which classes they map to.
-     *
-     * @var array
      */
-    public static $valueMap = [
+    public static array $valueMap = [
         'BINARY' => VObject\Property\Binary::class,
         'BOOLEAN' => VObject\Property\Boolean::class,
         'CAL-ADDRESS' => VObject\Property\ICalendar\CalAddress::class,
@@ -73,10 +70,8 @@ class VCalendar extends VObject\Document
 
     /**
      * List of properties, and which classes they map to.
-     *
-     * @var array
      */
-    public static $propertyMap = [
+    public static array $propertyMap = [
         // Calendar properties
         'CALSCALE' => VObject\Property\FlatText::class,
         'METHOD' => VObject\Property\FlatText::class,
@@ -154,10 +149,8 @@ class VCalendar extends VObject\Document
 
     /**
      * Returns the current document type.
-     *
-     * @return int
      */
-    public function getDocumentType()
+    public function getDocumentType(): int
     {
         return self::ICALENDAR20;
     }
@@ -169,13 +162,13 @@ public function getDocumentType()
      *
      * VTIMEZONE components will always be excluded.
      *
-     * @param string $componentName filter by component name
+     * @param string|null $componentName filter by component name
      *
      * @return VObject\Component[]
      */
-    public function getBaseComponents($componentName = null)
+    public function getBaseComponents(string $componentName = null): array
     {
-        $isBaseComponent = function ($component) {
+        $isBaseComponent = function ($component): bool {
             if (!$component instanceof VObject\Component) {
                 return false;
             }
@@ -220,13 +213,13 @@ public function getBaseComponents($componentName = null)
      *
      * If there is no such component, null will be returned.
      *
-     * @param string $componentName filter by component name
+     * @param string|null $componentName filter by component name
      *
      * @return VObject\Component|null
      */
-    public function getBaseComponent($componentName = null)
+    public function getBaseComponent(string $componentName = null): ?Component
     {
-        $isBaseComponent = function ($component) {
+        $isBaseComponent = function ($component): bool {
             if (!$component instanceof VObject\Component) {
                 return false;
             }
@@ -270,34 +263,35 @@ public function getBaseComponent($componentName = null)
      * can be used to expand the event into multiple sub-events.
      *
      * Each event will be stripped from its recurrence information, and only
-     * the instances of the event in the specified timerange will be left
+     * the instances of the event in the specified time range will be left
      * alone.
      *
      * In addition, this method will cause timezone information to be stripped,
      * and normalized to UTC.
      *
-     * @param DateTimeZone $timeZone reference timezone for floating dates and
-     *                               times
+     * @param \DateTimeZone|null $timeZone reference timezone for floating dates and
+     *                                     times
      *
-     * @return VCalendar
+     * @throws InvalidDataException
+     * @throws VObject\Recur\MaxInstancesExceededException
      */
-    public function expand(DateTimeInterface $start, DateTimeInterface $end, DateTimeZone $timeZone = null)
+    public function expand(\DateTimeInterface $start, \DateTimeInterface $end, \DateTimeZone $timeZone = null): VCalendar
     {
         $newChildren = [];
         $recurringEvents = [];
 
         if (!$timeZone) {
-            $timeZone = new DateTimeZone('UTC');
+            $timeZone = new \DateTimeZone('UTC');
         }
 
-        $stripTimezones = function (Component $component) use ($timeZone, &$stripTimezones) {
+        $stripTimezones = function (Component $component) use ($timeZone, &$stripTimezones): Component {
             foreach ($component->children() as $componentChild) {
                 if ($componentChild instanceof Property\ICalendar\DateTime && $componentChild->hasTime()) {
                     $dt = $componentChild->getDateTimes($timeZone);
                     // We only need to update the first timezone, because
                     // setDateTimes will match all other timezones to the
                     // first.
-                    $dt[0] = $dt[0]->setTimeZone(new DateTimeZone('UTC'));
+                    $dt[0] = $dt[0]->setTimeZone(new \DateTimeZone('UTC'));
                     $componentChild->setDateTimes($dt);
                 } elseif ($componentChild instanceof Component) {
                     $stripTimezones($componentChild);
@@ -356,10 +350,8 @@ public function expand(DateTimeInterface $start, DateTimeInterface $end, DateTim
 
     /**
      * This method should return a list of default property values.
-     *
-     * @return array
      */
-    protected function getDefaults()
+    protected function getDefaults(): array
     {
         return [
             'VERSION' => '2.0',
@@ -380,10 +372,8 @@ protected function getDefaults()
      *   * + - Must appear at least once.
      *   * * - Can appear any number of times.
      *   * ? - May appear, but not more than once.
-     *
-     * @var array
      */
-    public function getValidationRules()
+    public function getValidationRules(): array
     {
         return [
             'PRODID' => 1,
@@ -413,12 +403,8 @@ public function getValidationRules()
      *   1 - The issue was repaired (only happens if REPAIR was turned on).
      *   2 - A warning.
      *   3 - An error.
-     *
-     * @param int $options
-     *
-     * @return array
      */
-    public function validate($options = 0)
+    public function validate(int $options = 0): array
     {
         $warnings = parent::validate($options);
 
@@ -511,10 +497,8 @@ public function validate($options = 0)
 
     /**
      * Returns all components with a specific UID value.
-     *
-     * @return array
      */
-    public function getByUID($uid)
+    public function getByUID($uid): array
     {
         return array_filter($this->getComponents(), function ($item) use ($uid) {
             if (!$itemUid = $item->select('UID')) {
diff --git a/lib/Component/VCard.php b/lib/Component/VCard.php
index eac789842..0f2a5e266 100644
--- a/lib/Component/VCard.php
+++ b/lib/Component/VCard.php
@@ -14,6 +14,10 @@
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
+ *
+ * @property VObject\Property\FlatText FN
+ * @property VObject\Property\Text ORG
+ * @property VObject\Property\FlatText EMAIL
  */
 class VCard extends VObject\Document
 {
@@ -21,33 +25,25 @@ class VCard extends VObject\Document
      * The default name for this component.
      *
      * This should be 'VCALENDAR' or 'VCARD'.
-     *
-     * @var string
      */
-    public static $defaultName = 'VCARD';
+    public static ?string $defaultName = 'VCARD';
 
     /**
      * Caching the version number.
-     *
-     * @var int
      */
-    private $version = null;
+    private ?int $version = null;
 
     /**
      * This is a list of components, and which classes they should map to.
-     *
-     * @var array
      */
-    public static $componentMap = [
+    public static array $componentMap = [
         'VCARD' => VCard::class,
     ];
 
     /**
      * List of value-types, and which classes they map to.
-     *
-     * @var array
      */
-    public static $valueMap = [
+    public static array $valueMap = [
         'BINARY' => VObject\Property\Binary::class,
         'BOOLEAN' => VObject\Property\Boolean::class,
         'CONTENT-ID' => VObject\Property\FlatText::class,   // vCard 2.1 only
@@ -69,10 +65,8 @@ class VCard extends VObject\Document
 
     /**
      * List of properties, and which classes they map to.
-     *
-     * @var array
      */
-    public static $propertyMap = [
+    public static array $propertyMap = [
         // vCard 2.1 properties and up
         'N' => VObject\Property\Text::class,
         'FN' => VObject\Property\FlatText::class,
@@ -140,10 +134,8 @@ class VCard extends VObject\Document
 
     /**
      * Returns the current document type.
-     *
-     * @return int
      */
-    public function getDocumentType()
+    public function getDocumentType(): int
     {
         if (!$this->version) {
             $version = (string) $this->VERSION;
@@ -178,11 +170,9 @@ public function getDocumentType()
      *
      * If input and output version are identical, a clone is returned.
      *
-     * @param int $target
-     *
-     * @return VCard
+     * @throws VObject\InvalidDataException
      */
-    public function convert($target)
+    public function convert(int $target): VCard
     {
         $converter = new VObject\VCardConverter();
 
@@ -194,7 +184,7 @@ public function convert($target)
      *
      * If the VCARD doesn't know its version, 2.1 is assumed.
      */
-    const DEFAULT_VERSION = self::VCARD21;
+    public const DEFAULT_VERSION = self::VCARD21;
 
     /**
      * Validates the node for correctness.
@@ -213,12 +203,8 @@ public function convert($target)
      *   1 - The issue was repaired (only happens if REPAIR was turned on)
      *   2 - An inconsequential issue
      *   3 - A severe issue.
-     *
-     * @param int $options
-     *
-     * @return array
      */
-    public function validate($options = 0)
+    public function validate(int $options = 0): array
     {
         $warnings = [];
 
@@ -291,6 +277,11 @@ public function validate($options = 0)
                     $this->FN = (string) $this->ORG;
                     $repaired = true;
 
+                // Otherwise, the NICKNAME property may work
+                } elseif (isset($this->NICKNAME)) {
+                    $this->FN = (string) $this->NICKNAME;
+                    $repaired = true;
+
                 // Otherwise, the EMAIL property may work
                 } elseif (isset($this->EMAIL)) {
                     $this->FN = (string) $this->EMAIL;
@@ -322,10 +313,8 @@ public function validate($options = 0)
      *   * + - Must appear at least once.
      *   * * - Can appear any number of times.
      *   * ? - May appear, but not more than once.
-     *
-     * @var array
      */
-    public function getValidationRules()
+    public function getValidationRules(): array
     {
         return [
             'ADR' => '*',
@@ -379,12 +368,8 @@ public function getValidationRules()
      *
      * If neither of those parameters are specified, the first is returned, if
      * a field with that name does not exist, null is returned.
-     *
-     * @param string $fieldName
-     *
-     * @return VObject\Property|null
      */
-    public function preferred($propertyName)
+    public function preferred(string $propertyName): ?VObject\Property
     {
         $preferred = null;
         $lastPref = 101;
@@ -411,26 +396,23 @@ public function preferred($propertyName)
      * This function will return null if the property does not exist. If there are
      * multiple properties with the same TYPE value, only one will be returned.
      *
-     * @param string $propertyName
-     * @param string $type
-     *
-     * @return VObject\Property|null
+     * @return \ArrayAccess|array|null
      */
-    public function getByType($propertyName, $type)
+    public function getByType(string $propertyName, string $type)
     {
         foreach ($this->select($propertyName) as $field) {
             if (isset($field['TYPE']) && $field['TYPE']->has($type)) {
                 return $field;
             }
         }
+
+        return null;
     }
 
     /**
      * This method should return a list of default property values.
-     *
-     * @return array
      */
-    protected function getDefaults()
+    protected function getDefaults(): array
     {
         return [
             'VERSION' => '4.0',
@@ -442,11 +424,9 @@ protected function getDefaults()
     /**
      * This method returns an array, with the representation as it should be
      * encoded in json. This is used to create jCard or jCal documents.
-     *
-     * @return array
      */
     #[\ReturnTypeWillChange]
-    public function jsonSerialize()
+    public function jsonSerialize(): array
     {
         // A vcard does not have sub-components, so we're overriding this
         // method to remove that array element.
@@ -465,10 +445,8 @@ public function jsonSerialize()
     /**
      * This method serializes the data into XML. This is used to create xCard or
      * xCal documents.
-     *
-     * @param Xml\Writer $writer XML writer
      */
-    public function xmlSerialize(Xml\Writer $writer)
+    public function xmlSerialize(Xml\Writer $writer): void
     {
         $propertiesByGroup = [];
 
@@ -517,12 +495,8 @@ public function xmlSerialize(Xml\Writer $writer)
 
     /**
      * Returns the default class for a property name.
-     *
-     * @param string $propertyName
-     *
-     * @return string
      */
-    public function getClassNameForPropertyName($propertyName)
+    public function getClassNameForPropertyName(string $propertyName): string
     {
         $className = parent::getClassNameForPropertyName($propertyName);
 
diff --git a/lib/Component/VEvent.php b/lib/Component/VEvent.php
index 6ea93ed5e..e29e56322 100644
--- a/lib/Component/VEvent.php
+++ b/lib/Component/VEvent.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Component;
 
-use DateTimeInterface;
 use Sabre\VObject;
 use Sabre\VObject\Recur\EventIterator;
 use Sabre\VObject\Recur\NoInstancesException;
@@ -15,6 +14,18 @@
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
+ *
+ * @property VObject\Property\ICalendar\DateTime DTSTART
+ * @property VObject\Property\ICalendar\DateTime DTEND
+ * @property VObject\Property\ICalendar\DateTime DTSTAMP
+ * @property VObject\Property\ICalendar\Duration DURATION
+ * @property VObject\Property\ICalendar\Recur RRULE
+ * @property VObject\Property\ICalendar\DateTime[] EXDATE
+ * @property VObject\Property\ICalendar\DateTime RDATE
+ * @property VObject\Property\ICalendar\Recur EXRULE
+ * @property VObject\Property\ICalendar\DateTime RECURRENCE-ID
+ * @property VObject\Property\FlatText TRANSP
+ * @property VObject\Property\FlatText STATUS
  */
 class VEvent extends VObject\Component
 {
@@ -25,9 +36,10 @@ class VEvent extends VObject\Component
      * The rules used to determine if an event falls within the specified
      * time-range is based on the CalDAV specification.
      *
-     * @return bool
+     * @throws VObject\InvalidDataException
+     * @throws VObject\Recur\MaxInstancesExceededException
      */
-    public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
+    public function isInTimeRange(\DateTimeInterface $start, \DateTimeInterface $end): bool
     {
         if ($this->RRULE) {
             try {
@@ -44,14 +56,14 @@ public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
             // recurrence instance exceeded the start of the requested
             // time-range.
             //
-            // If the starttime of the recurrence did not exceed the
+            // If the start time of the recurrence did not exceed the
             // end of the time range as well, we have a match.
             return $it->getDTStart() < $end && $it->getDTEnd() > $start;
         }
 
         $effectiveStart = $this->DTSTART->getDateTime($start->getTimezone());
         if (isset($this->DTEND)) {
-            // The DTEND property is considered non inclusive. So for a 3 day
+            // The DTEND property is considered non-inclusive. So for a 3-day
             // event in july, dtstart and dtend would have to be July 1st and
             // July 4th respectively.
             //
@@ -73,10 +85,8 @@ public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
 
     /**
      * This method should return a list of default property values.
-     *
-     * @return array
      */
-    protected function getDefaults()
+    protected function getDefaults(): array
     {
         return [
             'UID' => 'sabre-vobject-'.VObject\UUIDUtil::getUUID(),
@@ -96,10 +106,8 @@ protected function getDefaults()
      *   * + - Must appear at least once.
      *   * * - Can appear any number of times.
      *   * ? - May appear, but not more than once.
-     *
-     * @var array
      */
-    public function getValidationRules()
+    public function getValidationRules(): array
     {
         $hasMethod = isset($this->parent->METHOD);
 
diff --git a/lib/Component/VFreeBusy.php b/lib/Component/VFreeBusy.php
index fef418b53..a9891c92c 100644
--- a/lib/Component/VFreeBusy.php
+++ b/lib/Component/VFreeBusy.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Component;
 
-use DateTimeInterface;
 use Sabre\VObject;
 
 /**
@@ -14,6 +13,8 @@
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
+ *
+ * @property VObject\Property\ICalendar\Period FREEBUSY
  */
 class VFreeBusy extends VObject\Component
 {
@@ -21,9 +22,9 @@ class VFreeBusy extends VObject\Component
      * Checks based on the contained FREEBUSY information, if a timeslot is
      * available.
      *
-     * @return bool
+     * @throws VObject\InvalidDataException
      */
-    public function isFree(DateTimeInterface $start, DatetimeInterface $end)
+    public function isFree(\DateTimeInterface $start, \DatetimeInterface $end): bool
     {
         foreach ($this->select('FREEBUSY') as $freebusy) {
             // We are only interested in FBTYPE=BUSY (the default),
@@ -69,10 +70,8 @@ public function isFree(DateTimeInterface $start, DatetimeInterface $end)
      *   * + - Must appear at least once.
      *   * * - Can appear any number of times.
      *   * ? - May appear, but not more than once.
-     *
-     * @var array
      */
-    public function getValidationRules()
+    public function getValidationRules(): array
     {
         return [
             'UID' => 1,
diff --git a/lib/Component/VJournal.php b/lib/Component/VJournal.php
index 9b7f1b873..30e40adf7 100644
--- a/lib/Component/VJournal.php
+++ b/lib/Component/VJournal.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Component;
 
-use DateTimeInterface;
 use Sabre\VObject;
 
 /**
@@ -13,6 +12,8 @@
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
+ *
+ * @property VObject\Property\ICalendar\DateTime DTSTART
  */
 class VJournal extends VObject\Component
 {
@@ -23,9 +24,9 @@ class VJournal extends VObject\Component
      * The rules used to determine if an event falls within the specified
      * time-range is based on the CalDAV specification.
      *
-     * @return bool
+     * @throws VObject\InvalidDataException
      */
-    public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
+    public function isInTimeRange(\DateTimeInterface $start, \DateTimeInterface $end): bool
     {
         $dtstart = isset($this->DTSTART) ? $this->DTSTART->getDateTime() : null;
         if ($dtstart) {
@@ -52,10 +53,8 @@ public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
      *   * + - Must appear at least once.
      *   * * - Can appear any number of times.
      *   * ? - May appear, but not more than once.
-     *
-     * @var array
      */
-    public function getValidationRules()
+    public function getValidationRules(): array
     {
         return [
             'UID' => 1,
@@ -88,10 +87,8 @@ public function getValidationRules()
 
     /**
      * This method should return a list of default property values.
-     *
-     * @return array
      */
-    protected function getDefaults()
+    protected function getDefaults(): array
     {
         return [
             'UID' => 'sabre-vobject-'.VObject\UUIDUtil::getUUID(),
diff --git a/lib/Component/VTimeZone.php b/lib/Component/VTimeZone.php
index 21c062377..9dcf9b976 100644
--- a/lib/Component/VTimeZone.php
+++ b/lib/Component/VTimeZone.php
@@ -2,6 +2,7 @@
 
 namespace Sabre\VObject\Component;
 
+use DateTimeZone;
 use Sabre\VObject;
 
 /**
@@ -13,6 +14,8 @@
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
+ *
+ * @property VObject\Property\FlatText TZID
  */
 class VTimeZone extends VObject\Component
 {
@@ -21,10 +24,8 @@ class VTimeZone extends VObject\Component
      *
      * If we can't accurately determine the timezone, this method will return
      * UTC.
-     *
-     * @return \DateTimeZone
      */
-    public function getTimeZone()
+    public function getTimeZone(): \DateTimeZone
     {
         return VObject\TimeZoneUtil::getTimeZone((string) $this->TZID, $this->root);
     }
@@ -41,10 +42,8 @@ public function getTimeZone()
      *   * + - Must appear at least once.
      *   * * - Can appear any number of times.
      *   * ? - May appear, but not more than once.
-     *
-     * @var array
      */
-    public function getValidationRules()
+    public function getValidationRules(): array
     {
         return [
             'TZID' => 1,
diff --git a/lib/Component/VTodo.php b/lib/Component/VTodo.php
index 6f022ba6d..bda49da74 100644
--- a/lib/Component/VTodo.php
+++ b/lib/Component/VTodo.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Component;
 
-use DateTimeInterface;
 use Sabre\VObject;
 
 /**
@@ -13,6 +12,19 @@
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
+ *
+ * @property VObject\Property\ICalendar\DateTime DTSTART
+ * @property VObject\Property\ICalendar\DateTime DTEND
+ * @property VObject\Property\ICalendar\DateTime DTSTAMP
+ * @property VObject\Property\ICalendar\Duration DURATION
+ * @property VObject\Property\ICalendar\Recur RRULE
+ * @property VObject\Property\ICalendar\DateTime EXDATE
+ * @property VObject\Property\ICalendar\DateTime RDATE
+ * @property VObject\Property\ICalendar\Recur EXRULE
+ * @property VObject\Property\ICalendar\DateTime {'RECURRENCE-ID'}
+ * @property VObject\Property\ICalendar\DateTime DUE
+ * @property VObject\Property\ICalendar\DateTime COMPLETED
+ * @property VObject\Property\ICalendar\DateTime CREATED
  */
 class VTodo extends VObject\Component
 {
@@ -23,9 +35,9 @@ class VTodo extends VObject\Component
      * The rules used to determine if an event falls within the specified
      * time-range is based on the CalDAV specification.
      *
-     * @return bool
+     * @throws VObject\InvalidDataException
      */
-    public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
+    public function isInTimeRange(\DateTimeInterface $start, \DateTimeInterface $end): bool
     {
         $dtstart = isset($this->DTSTART) ? $this->DTSTART->getDateTime() : null;
         $duration = isset($this->DURATION) ? VObject\DateTimeParser::parseDuration($this->DURATION) : null;
@@ -40,8 +52,8 @@ public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
                 return $start <= $effectiveEnd && $end > $dtstart;
             } elseif ($due) {
                 return
-                    ($start < $due || $start <= $dtstart) &&
-                    ($end > $dtstart || $end >= $due);
+                    ($start < $due || $start <= $dtstart)
+                    && ($end > $dtstart || $end >= $due);
             } else {
                 return $start <= $dtstart && $end > $dtstart;
             }
@@ -51,8 +63,8 @@ public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
         }
         if ($completed && $created) {
             return
-                ($start <= $created || $start <= $completed) &&
-                ($end >= $created || $end >= $completed);
+                ($start <= $created || $start <= $completed)
+                && ($end >= $created || $end >= $completed);
         }
         if ($completed) {
             return $start <= $completed && $end >= $completed;
@@ -76,10 +88,8 @@ public function isInTimeRange(DateTimeInterface $start, DateTimeInterface $end)
      *   * + - Must appear at least once.
      *   * * - Can appear any number of times.
      *   * ? - May appear, but not more than once.
-     *
-     * @var array
      */
-    public function getValidationRules()
+    public function getValidationRules(): array
     {
         return [
             'UID' => 1,
@@ -137,11 +147,9 @@ public function getValidationRules()
      *   2 - An inconsequential issue
      *   3 - A severe issue.
      *
-     * @param int $options
-     *
-     * @return array
+     * @throws VObject\InvalidDataException
      */
-    public function validate($options = 0)
+    public function validate(int $options = 0): array
     {
         $result = parent::validate($options);
         if (isset($this->DUE) && isset($this->DTSTART)) {
@@ -168,10 +176,8 @@ public function validate($options = 0)
 
     /**
      * This method should return a list of default property values.
-     *
-     * @return array
      */
-    protected function getDefaults()
+    protected function getDefaults(): array
     {
         return [
             'UID' => 'sabre-vobject-'.VObject\UUIDUtil::getUUID(),
diff --git a/lib/DateTimeParser.php b/lib/DateTimeParser.php
index 1c253437a..5ce9f207a 100644
--- a/lib/DateTimeParser.php
+++ b/lib/DateTimeParser.php
@@ -4,12 +4,11 @@
 
 use DateInterval;
 use DateTimeImmutable;
-use DateTimeZone;
 
 /**
  * DateTimeParser.
  *
- * This class is responsible for parsing the several different date and time
+ * This class is responsible for parsing the several date and time
  * formats iCalendar and vCards have.
  *
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
@@ -26,12 +25,9 @@ class DateTimeParser
      * if the non-UTC format is used. The argument is used as a reference, the
      * returned DateTimeImmutable object will still be in the UTC timezone.
      *
-     * @param string       $dt
-     * @param DateTimeZone $tz
-     *
-     * @return DateTimeImmutable
+     * @throws InvalidDataException
      */
-    public static function parseDateTime($dt, DateTimeZone $tz = null)
+    public static function parseDateTime(string $dt, \DateTimeZone $tz = null): \DateTimeImmutable
     {
         // Format is YYYYMMDD + "T" + hhmmss
         $result = preg_match('/^([0-9]{4})([0-1][0-9])([0-3][0-9])T([0-2][0-9])([0-5][0-9])([0-5][0-9])([Z]?)$/', $dt, $matches);
@@ -41,11 +37,11 @@ public static function parseDateTime($dt, DateTimeZone $tz = null)
         }
 
         if ('Z' === $matches[7] || is_null($tz)) {
-            $tz = new DateTimeZone('UTC');
+            $tz = new \DateTimeZone('UTC');
         }
 
         try {
-            $date = new DateTimeImmutable($matches[1].'-'.$matches[2].'-'.$matches[3].' '.$matches[4].':'.$matches[5].':'.$matches[6], $tz);
+            $date = new \DateTimeImmutable($matches[1].'-'.$matches[2].'-'.$matches[3].' '.$matches[4].':'.$matches[5].':'.$matches[6], $tz);
         } catch (\Exception $e) {
             throw new InvalidDataException('The supplied iCalendar datetime value is incorrect: '.$dt);
         }
@@ -56,12 +52,9 @@ public static function parseDateTime($dt, DateTimeZone $tz = null)
     /**
      * Parses an iCalendar (rfc5545) formatted date and returns a DateTimeImmutable object.
      *
-     * @param string       $date
-     * @param DateTimeZone $tz
-     *
-     * @return DateTimeImmutable
+     * @throws InvalidDataException
      */
-    public static function parseDate($date, DateTimeZone $tz = null)
+    public static function parseDate(string $date, \DateTimeZone $tz = null): \DateTimeImmutable
     {
         // Format is YYYYMMDD
         $result = preg_match('/^([0-9]{4})([0-1][0-9])([0-3][0-9])$/', $date, $matches);
@@ -71,11 +64,11 @@ public static function parseDate($date, DateTimeZone $tz = null)
         }
 
         if (is_null($tz)) {
-            $tz = new DateTimeZone('UTC');
+            $tz = new \DateTimeZone('UTC');
         }
 
         try {
-            $date = new DateTimeImmutable($matches[1].'-'.$matches[2].'-'.$matches[3], $tz);
+            $date = new \DateTimeImmutable($matches[1].'-'.$matches[2].'-'.$matches[3], $tz);
         } catch (\Exception $e) {
             throw new InvalidDataException('The supplied iCalendar date value is incorrect: '.$date);
         }
@@ -86,29 +79,25 @@ public static function parseDate($date, DateTimeZone $tz = null)
     /**
      * Parses an iCalendar (RFC5545) formatted duration value.
      *
-     * This method will either return a DateTimeInterval object, or a string
-     * suitable for strtotime or DateTime::modify.
-     *
-     * @param string $duration
-     * @param bool   $asString
+     * This method will return a DateTimeInterval object
      *
-     * @return DateInterval|string
+     * @throws InvalidDataException
+     * @throws \Exception
      */
-    public static function parseDuration($duration, $asString = false)
+    public static function parseDuration(string $duration): \DateInterval
     {
         $result = preg_match('/^(?<plusminus>\+|-)?P((?<week>\d+)W)?((?<day>\d+)D)?(T((?<hour>\d+)H)?((?<minute>\d+)M)?((?<second>\d+)S)?)?$/', $duration, $matches);
         if (!$result) {
             throw new InvalidDataException('The supplied iCalendar duration value is incorrect: '.$duration);
         }
 
-        if (!$asString) {
-            $invert = false;
+        $invert = false;
 
-            if ('-' === $matches['plusminus']) {
-                $invert = true;
-            }
+        if (isset($matches['plusminus']) && '-' === $matches['plusminus']) {
+            $invert = true;
+        }
 
-            $parts = [
+        $parts = [
                 'week',
                 'day',
                 'hour',
@@ -116,50 +105,64 @@ public static function parseDuration($duration, $asString = false)
                 'second',
             ];
 
-            foreach ($parts as $part) {
-                $matches[$part] = isset($matches[$part]) && $matches[$part] ? (int) $matches[$part] : 0;
-            }
-
-            // We need to re-construct the $duration string, because weeks and
-            // days are not supported by DateInterval in the same string.
-            $duration = 'P';
-            $days = $matches['day'];
+        foreach ($parts as $part) {
+            $matches[$part] = isset($matches[$part]) && $matches[$part] ? (int) $matches[$part] : 0;
+        }
 
-            if ($matches['week']) {
-                $days += $matches['week'] * 7;
-            }
+        // We need to re-construct the $duration string, because weeks and
+        // days are not supported by DateInterval in the same string.
+        $duration = 'P';
+        $days = $matches['day'];
 
-            if ($days) {
-                $duration .= $days.'D';
-            }
+        if ($matches['week']) {
+            $days += $matches['week'] * 7;
+        }
 
-            if ($matches['minute'] || $matches['second'] || $matches['hour']) {
-                $duration .= 'T';
+        if ($days) {
+            $duration .= $days.'D';
+        }
 
-                if ($matches['hour']) {
-                    $duration .= $matches['hour'].'H';
-                }
+        if ($matches['minute'] || $matches['second'] || $matches['hour']) {
+            $duration .= 'T';
 
-                if ($matches['minute']) {
-                    $duration .= $matches['minute'].'M';
-                }
+            if ($matches['hour']) {
+                $duration .= $matches['hour'].'H';
+            }
 
-                if ($matches['second']) {
-                    $duration .= $matches['second'].'S';
-                }
+            if ($matches['minute']) {
+                $duration .= $matches['minute'].'M';
             }
 
-            if ('P' === $duration) {
-                $duration = 'PT0S';
+            if ($matches['second']) {
+                $duration .= $matches['second'].'S';
             }
+        }
 
-            $iv = new DateInterval($duration);
+        if ('P' === $duration) {
+            $duration = 'PT0S';
+        }
 
-            if ($invert) {
-                $iv->invert = true;
-            }
+        $iv = new \DateInterval($duration);
 
-            return $iv;
+        if ($invert) {
+            $iv->invert = true;
+        }
+
+        return $iv;
+    }
+
+    /**
+     * Parses an iCalendar (RFC5545) formatted duration value.
+     *
+     * This method will return a string suitable for strtotime or DateTime::modify.
+     *
+     * @throws InvalidDataException
+     */
+    public static function parseDurationAsString(string $duration): string
+    {
+        $result = preg_match('/^(?<plusminus>\+|-)?P((?<week>\d+)W)?((?<day>\d+)D)?(T((?<hour>\d+)H)?((?<minute>\d+)M)?((?<second>\d+)S)?)?$/', $duration, $matches);
+        if (!$result) {
+            throw new InvalidDataException('The supplied iCalendar duration value is incorrect: '.$duration);
         }
 
         $parts = [
@@ -190,12 +193,13 @@ public static function parseDuration($duration, $asString = false)
     /**
      * Parses either a Date or DateTime, or Duration value.
      *
-     * @param string              $date
-     * @param DateTimeZone|string $referenceTz
+     * @param \DateTimeZone|string $referenceTz
      *
-     * @return DateTimeImmutable|DateInterval
+     * @return \DateInterval|\DateTimeImmutable
+     *
+     * @throws InvalidDataException
      */
-    public static function parse($date, $referenceTz = null)
+    public static function parse(string $date, $referenceTz = null)
     {
         if ('P' === $date[0] || ('-' === $date[0] && 'P' === $date[1])) {
             return self::parseDuration($date);
@@ -258,11 +262,9 @@ public static function parse($date, $referenceTz = null)
      * Times may be postfixed by a timezone offset. This can be either 'Z' for
      * UTC, or a string like -0500 or +1100.
      *
-     * @param string $date
-     *
-     * @return array
+     * @throws InvalidDataException
      */
-    public static function parseVCardDateTime($date)
+    public static function parseVCardDateTime(string $date): array
     {
         $regex = '/^
             (?:  # date part
@@ -377,11 +379,9 @@ public static function parseVCardDateTime($date)
      * Times may be postfixed by a timezone offset. This can be either 'Z' for
      * UTC, or a string like -0500 or +11:00.
      *
-     * @param string $date
-     *
-     * @return array
+     * @throws InvalidDataException
      */
-    public static function parseVCardTime($date)
+    public static function parseVCardTime(string $date): array
     {
         $regex = '/^
             (?<hour> [0-9]{2} | -)
@@ -483,11 +483,9 @@ public static function parseVCardTime($date)
      * Times may be postfixed by a timezone offset. This can be either 'Z' for
      * UTC, or a string like -0500 or +1100.
      *
-     * @param string $date
-     *
-     * @return array
+     * @throws InvalidDataException
      */
-    public static function parseVCardDateAndOrTime($date)
+    public static function parseVCardDateAndOrTime(string $date): array
     {
         // \d{8}|\d{4}-\d\d|--\d\d(\d\d)?|---\d\d
         $valueDate = '/^(?J)(?:'.
diff --git a/lib/Document.php b/lib/Document.php
index 6265f34b5..2a249580b 100644
--- a/lib/Document.php
+++ b/lib/Document.php
@@ -2,6 +2,8 @@
 
 namespace Sabre\VObject;
 
+use Sabre\VObject;
+
 /**
  * Document.
  *
@@ -15,68 +17,62 @@
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
+ *
+ * @property VObject\Property\FlatText VERSION
  */
 abstract class Document extends Component
 {
     /**
      * Unknown document type.
      */
-    const UNKNOWN = 1;
+    public const UNKNOWN = 1;
 
     /**
      * vCalendar 1.0.
      */
-    const VCALENDAR10 = 2;
+    public const VCALENDAR10 = 2;
 
     /**
      * iCalendar 2.0.
      */
-    const ICALENDAR20 = 3;
+    public const ICALENDAR20 = 3;
 
     /**
      * vCard 2.1.
      */
-    const VCARD21 = 4;
+    public const VCARD21 = 4;
 
     /**
      * vCard 3.0.
      */
-    const VCARD30 = 5;
+    public const VCARD30 = 5;
 
     /**
      * vCard 4.0.
      */
-    const VCARD40 = 6;
+    public const VCARD40 = 6;
 
     /**
      * The default name for this component.
      *
      * This should be 'VCALENDAR' or 'VCARD'.
-     *
-     * @var string
      */
-    public static $defaultName;
+    public static ?string $defaultName = null;
 
     /**
      * List of properties, and which classes they map to.
-     *
-     * @var array
      */
-    public static $propertyMap = [];
+    public static array $propertyMap = [];
 
     /**
      * List of components, along with which classes they map to.
-     *
-     * @var array
      */
-    public static $componentMap = [];
+    public static array $componentMap = [];
 
     /**
      * List of value-types, and which classes they map to.
-     *
-     * @var array
      */
-    public static $valueMap = [];
+    public static array $valueMap = [];
 
     /**
      * Creates a new document.
@@ -97,22 +93,20 @@ public function __construct()
         $args = func_get_args();
         $name = static::$defaultName;
         if (0 === count($args) || is_array($args[0])) {
-            $children = isset($args[0]) ? $args[0] : [];
-            $defaults = isset($args[1]) ? $args[1] : true;
+            $children = $args[0] ?? [];
+            $defaults = $args[1] ?? true;
         } else {
             $name = $args[0];
-            $children = isset($args[1]) ? $args[1] : [];
-            $defaults = isset($args[2]) ? $args[2] : true;
+            $children = $args[1] ?? [];
+            $defaults = $args[2] ?? true;
         }
         parent::__construct($this, $name, $children, $defaults);
     }
 
     /**
      * Returns the current document type.
-     *
-     * @return int
      */
-    public function getDocumentType()
+    public function getDocumentType(): int
     {
         return self::UNKNOWN;
     }
@@ -122,13 +116,8 @@ public function getDocumentType()
      *
      * If it's a known component, we will automatically call createComponent.
      * otherwise, we'll assume it's a property and call createProperty instead.
-     *
-     * @param string $name
-     * @param string $arg1,... Unlimited number of args
-     *
-     * @return mixed
      */
-    public function create($name)
+    public function create(string $name)
     {
         if (isset(static::$componentMap[strtoupper($name)])) {
             return call_user_func_array([$this, 'createComponent'], func_get_args());
@@ -150,14 +139,8 @@ public function create($name)
      * By default, a set of sensible values will be added to the component. For
      * an iCalendar object, this may be something like CALSCALE:GREGORIAN. To
      * ensure that this does not happen, set $defaults to false.
-     *
-     * @param string $name
-     * @param array  $children
-     * @param bool   $defaults
-     *
-     * @return Component
      */
-    public function createComponent($name, array $children = null, $defaults = true)
+    public function createComponent(string $name, array $children = null, bool $defaults = true): Component
     {
         $name = strtoupper($name);
         $class = Component::class;
@@ -182,16 +165,13 @@ public function createComponent($name, array $children = null, $defaults = true)
      * parameters will automatically be created, or you can just pass a list of
      * Parameter objects.
      *
-     * @param string $name
-     * @param mixed  $value
-     * @param array  $parameters
-     * @param string $valueType  Force a specific valuetype, such as URI or TEXT
+     * @param string|null $valueType Force a specific valueType, such as URI or TEXT
      *
-     * @return Property
+     * @throws InvalidDataException
      */
-    public function createProperty($name, $value = null, array $parameters = null, $valueType = null)
+    public function createProperty(string $name, $value = null, array $parameters = null, string $valueType = null): Property
     {
-        // If there's a . in the name, it means it's prefixed by a groupname.
+        // If there's a . in the name, it means it's prefixed by a group name.
         if (false !== ($i = strpos($name, '.'))) {
             $group = substr($name, 0, $i);
             $name = strtoupper(substr($name, $i + 1));
@@ -237,11 +217,9 @@ public function createProperty($name, $value = null, array $parameters = null, $
      *
      * This method returns null if we don't have a specialized class.
      *
-     * @param string $valueParam
-     *
-     * @return string|null
+     * @return string|void|null
      */
-    public function getClassNameForPropertyValue($valueParam)
+    public function getClassNameForPropertyValue(string $valueParam)
     {
         $valueParam = strtoupper($valueParam);
         if (isset(static::$valueMap[$valueParam])) {
@@ -251,17 +229,9 @@ public function getClassNameForPropertyValue($valueParam)
 
     /**
      * Returns the default class for a property name.
-     *
-     * @param string $propertyName
-     *
-     * @return string
      */
-    public function getClassNameForPropertyName($propertyName)
+    public function getClassNameForPropertyName(string $propertyName): string
     {
-        if (isset(static::$propertyMap[$propertyName])) {
-            return static::$propertyMap[$propertyName];
-        } else {
-            return Property\Unknown::class;
-        }
+        return static::$propertyMap[$propertyName] ?? Property\Unknown::class;
     }
 }
diff --git a/lib/ElementList.php b/lib/ElementList.php
index 860512649..9c81b7748 100644
--- a/lib/ElementList.php
+++ b/lib/ElementList.php
@@ -2,9 +2,6 @@
 
 namespace Sabre\VObject;
 
-use ArrayIterator;
-use LogicException;
-
 /**
  * VObject ElementList.
  *
@@ -15,20 +12,19 @@
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
  */
-class ElementList extends ArrayIterator
+class ElementList extends \ArrayIterator
 {
     /* {{{ ArrayAccess Interface */
 
     /**
      * Sets an item through ArrayAccess.
      *
-     * @param int   $offset
-     * @param mixed $value
+     * @param int $offset
      */
     #[\ReturnTypeWillChange]
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
-        throw new LogicException('You can not add new objects to an ElementList');
+        throw new \LogicException('You can not add new objects to an ElementList');
     }
 
     /**
@@ -39,9 +35,9 @@ public function offsetSet($offset, $value)
      * @param int $offset
      */
     #[\ReturnTypeWillChange]
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
-        throw new LogicException('You can not remove objects from an ElementList');
+        throw new \LogicException('You can not remove objects from an ElementList');
     }
 
     /* }}} */
diff --git a/lib/FreeBusyData.php b/lib/FreeBusyData.php
index 4d9f441ce..405a5886d 100644
--- a/lib/FreeBusyData.php
+++ b/lib/FreeBusyData.php
@@ -13,26 +13,20 @@ class FreeBusyData
 {
     /**
      * Start timestamp.
-     *
-     * @var int
      */
-    protected $start;
+    protected int $start;
 
     /**
      * End timestamp.
-     *
-     * @var int
      */
-    protected $end;
+    protected int $end;
 
     /**
      * A list of free-busy times.
-     *
-     * @var array
      */
-    protected $data;
+    protected array $data;
 
-    public function __construct($start, $end)
+    public function __construct(int $start, int $end)
     {
         $this->start = $start;
         $this->end = $end;
@@ -46,16 +40,14 @@ public function __construct($start, $end)
     }
 
     /**
-     * Adds free or busytime to the data.
+     * Adds free or busy time to the data.
      *
-     * @param int    $start
-     * @param int    $end
-     * @param string $type  FREE, BUSY, BUSY-UNAVAILABLE or BUSY-TENTATIVE
+     * @param string $type FREE, BUSY, BUSY-UNAVAILABLE or BUSY-TENTATIVE
      */
-    public function add($start, $end, $type)
+    public function add(int $start, int $end, string $type): void
     {
         if ($start > $this->end || $end < $this->start) {
-            // This new data is outside our timerange.
+            // This new data is outside our time range.
             return;
         }
 
@@ -178,7 +170,7 @@ public function add($start, $end, $type)
         }
     }
 
-    public function getData()
+    public function getData(): array
     {
         return $this->data;
     }
diff --git a/lib/FreeBusyGenerator.php b/lib/FreeBusyGenerator.php
index 81b8126d5..2f222e4e5 100644
--- a/lib/FreeBusyGenerator.php
+++ b/lib/FreeBusyGenerator.php
@@ -2,10 +2,10 @@
 
 namespace Sabre\VObject;
 
-use DateTimeImmutable;
-use DateTimeInterface;
-use DateTimeZone;
 use Sabre\VObject\Component\VCalendar;
+use Sabre\VObject\Component\VEvent;
+use Sabre\VObject\Component\VFreeBusy;
+use Sabre\VObject\Property\ICalendar\DateTime;
 use Sabre\VObject\Recur\EventIterator;
 use Sabre\VObject\Recur\NoInstancesException;
 
@@ -27,31 +27,23 @@ class FreeBusyGenerator
 {
     /**
      * Input objects.
-     *
-     * @var array
      */
-    protected $objects = [];
+    protected array $objects = [];
 
     /**
      * Start of range.
-     *
-     * @var DateTimeInterface|null
      */
-    protected $start;
+    protected ?\DateTimeInterface $start;
 
     /**
      * End of range.
-     *
-     * @var DateTimeInterface|null
      */
-    protected $end;
+    protected ?\DateTimeInterface $end;
 
     /**
      * VCALENDAR object.
-     *
-     * @var Document
      */
-    protected $baseObject;
+    protected ?Document $baseObject = null;
 
     /**
      * Reference timezone.
@@ -63,33 +55,24 @@ class FreeBusyGenerator
      * This is also used for all-day events.
      *
      * This defaults to UTC.
-     *
-     * @var DateTimeZone
      */
-    protected $timeZone;
+    protected \DateTimeZone $timeZone;
 
     /**
      * A VAVAILABILITY document.
      *
      * If this is set, its information will be included when calculating
      * freebusy time.
-     *
-     * @var Document
      */
-    protected $vavailability;
+    protected ?Document $vavailability = null;
 
     /**
      * Creates the generator.
      *
      * Check the setTimeRange and setObjects methods for details about the
      * arguments.
-     *
-     * @param DateTimeInterface $start
-     * @param DateTimeInterface $end
-     * @param mixed             $objects
-     * @param DateTimeZone      $timeZone
      */
-    public function __construct(DateTimeInterface $start = null, DateTimeInterface $end = null, $objects = null, DateTimeZone $timeZone = null)
+    public function __construct(\DateTimeInterface $start = null, \DateTimeInterface $end = null, $objects = null, \DateTimeZone $timeZone = null)
     {
         $this->setTimeRange($start, $end);
 
@@ -97,7 +80,7 @@ public function __construct(DateTimeInterface $start = null, DateTimeInterface $
             $this->setObjects($objects);
         }
         if (is_null($timeZone)) {
-            $timeZone = new DateTimeZone('UTC');
+            $timeZone = new \DateTimeZone('UTC');
         }
         $this->setTimeZone($timeZone);
     }
@@ -110,7 +93,7 @@ public function __construct(DateTimeInterface $start = null, DateTimeInterface $
      *
      * The VFREEBUSY object will be automatically added though.
      */
-    public function setBaseObject(Document $vcalendar)
+    public function setBaseObject(Document $vcalendar): void
     {
         $this->baseObject = $vcalendar;
     }
@@ -118,7 +101,7 @@ public function setBaseObject(Document $vcalendar)
     /**
      * Sets a VAVAILABILITY document.
      */
-    public function setVAvailability(Document $vcalendar)
+    public function setVAvailability(Document $vcalendar): void
     {
         $this->vavailability = $vcalendar;
     }
@@ -129,10 +112,8 @@ public function setVAvailability(Document $vcalendar)
      * You must either specify a vcalendar object as a string, or as the parse
      * Component.
      * It's also possible to specify multiple objects as an array.
-     *
-     * @param mixed $objects
      */
-    public function setObjects($objects)
+    public function setObjects($objects): void
     {
         if (!is_array($objects)) {
             $objects = [$objects];
@@ -153,18 +134,17 @@ public function setObjects($objects)
     /**
      * Sets the time range.
      *
-     * Any freebusy object falling outside of this time range will be ignored.
+     * Any freebusy object falling outside this time range will be ignored.
      *
-     * @param DateTimeInterface $start
-     * @param DateTimeInterface $end
+     * @throws \Exception
      */
-    public function setTimeRange(DateTimeInterface $start = null, DateTimeInterface $end = null)
+    public function setTimeRange(\DateTimeInterface $start = null, \DateTimeInterface $end = null): void
     {
         if (!$start) {
-            $start = new DateTimeImmutable(Settings::$minDate);
+            $start = new \DateTimeImmutable(Settings::$minDate);
         }
         if (!$end) {
-            $end = new DateTimeImmutable(Settings::$maxDate);
+            $end = new \DateTimeImmutable(Settings::$maxDate);
         }
         $this->start = $start;
         $this->end = $end;
@@ -173,7 +153,7 @@ public function setTimeRange(DateTimeInterface $start = null, DateTimeInterface
     /**
      * Sets the reference timezone for floating times.
      */
-    public function setTimeZone(DateTimeZone $timeZone)
+    public function setTimeZone(\DateTimeZone $timeZone): void
     {
         $this->timeZone = $timeZone;
     }
@@ -181,16 +161,14 @@ public function setTimeZone(DateTimeZone $timeZone)
     /**
      * Parses the input data and returns a correct VFREEBUSY object, wrapped in
      * a VCALENDAR.
-     *
-     * @return Component
      */
-    public function getResult()
+    public function getResult(): Component
     {
         $fbData = new FreeBusyData(
             $this->start->getTimeStamp(),
             $this->end->getTimeStamp()
         );
-        if ($this->vavailability) {
+        if (null !== $this->vavailability) {
             $this->calculateAvailability($fbData, $this->vavailability);
         }
 
@@ -203,7 +181,7 @@ public function getResult()
      * This method takes a VAVAILABILITY component and figures out all the
      * available times.
      */
-    protected function calculateAvailability(FreeBusyData $fbData, VCalendar $vavailability)
+    protected function calculateAvailability(FreeBusyData $fbData, VCalendar $vavailability): void
     {
         $vavailComps = iterator_to_array($vavailability->VAVAILABILITY);
         usort(
@@ -231,7 +209,7 @@ function ($a, $b) {
         // Now we go over all the VAVAILABILITY components and figure if
         // there's any we don't need to consider.
         //
-        // This is can be because of one of two reasons: either the
+        // This is because of one of two reasons: either the
         // VAVAILABILITY component falls outside the time we are interested in,
         // or a different VAVAILABILITY component with a higher priority has
         // already completely covered the time-range.
@@ -241,7 +219,7 @@ function ($a, $b) {
         foreach ($old as $vavail) {
             list($compStart, $compEnd) = $vavail->getEffectiveStartEnd();
 
-            // We don't care about datetimes that are earlier or later than the
+            // We don't care about date-times that are earlier or later than the
             // start and end of the freebusy report, so this gets normalized
             // first.
             if (is_null($compStart) || $compStart < $this->start) {
@@ -251,7 +229,7 @@ function ($a, $b) {
                 $compEnd = $this->end;
             }
 
-            // If the item fell out of the timerange, we can just skip it.
+            // If the item fell out of the time range, we can just skip it.
             if ($compStart > $this->end || $compEnd < $this->start) {
                 continue;
             }
@@ -261,8 +239,8 @@ function ($a, $b) {
             foreach ($new as $higherVavail) {
                 list($higherStart, $higherEnd) = $higherVavail->getEffectiveStartEnd();
                 if (
-                    (is_null($higherStart) || $higherStart < $compStart) &&
-                    (is_null($higherEnd) || $higherEnd > $compEnd)
+                    (is_null($higherStart) || $higherStart < $compStart)
+                    && (is_null($higherEnd) || $higherEnd > $compEnd)
                 ) {
                     // Component is fully covered by a higher priority
                     // component. We can skip this component.
@@ -305,18 +283,18 @@ function ($a, $b) {
                 foreach ($vavail->AVAILABLE as $available) {
                     list($availStart, $availEnd) = $available->getEffectiveStartEnd();
                     $fbData->add(
-                    $availStart->getTimeStamp(),
-                    $availEnd->getTimeStamp(),
-                    'FREE'
-                );
+                        $availStart->getTimeStamp(),
+                        $availEnd->getTimeStamp(),
+                        'FREE'
+                    );
 
                     if ($available->RRULE) {
                         // Our favourite thing: recurrence!!
 
                         $rruleIterator = new Recur\RRuleIterator(
-                        $available->RRULE->getValue(),
-                        $availStart
-                    );
+                            $available->RRULE->getValue(),
+                            $availStart
+                        );
                         $rruleIterator->fastForward($vavailStart);
 
                         $startEndDiff = $availStart->diff($availEnd);
@@ -326,7 +304,7 @@ function ($a, $b) {
                             $recurEnd = $recurStart->add($startEndDiff);
 
                             if ($recurStart > $vavailEnd) {
-                                // We're beyond the legal timerange.
+                                // We're beyond the legal time range.
                                 break;
                             }
 
@@ -337,10 +315,10 @@ function ($a, $b) {
                             }
 
                             $fbData->add(
-                            $recurStart->getTimeStamp(),
-                            $recurEnd->getTimeStamp(),
-                            'FREE'
-                        );
+                                $recurStart->getTimeStamp(),
+                                $recurEnd->getTimeStamp(),
+                                'FREE'
+                            );
 
                             $rruleIterator->next();
                         }
@@ -355,13 +333,16 @@ function ($a, $b) {
      * times on fbData.
      *
      * @param VCalendar[] $objects
+     *
+     * @throws InvalidDataException|Recur\MaxInstancesExceededException
      */
-    protected function calculateBusy(FreeBusyData $fbData, array $objects)
+    protected function calculateBusy(FreeBusyData $fbData, array $objects): void
     {
         foreach ($objects as $key => $object) {
             foreach ($object->getBaseComponents() as $component) {
                 switch ($component->name) {
                     case 'VEVENT':
+                        /** @var VEvent $component */
                         $FBTYPE = 'BUSY';
                         if (isset($component->TRANSP) && ('TRANSPARENT' === strtoupper($component->TRANSP))) {
                             break;
@@ -447,6 +428,7 @@ protected function calculateBusy(FreeBusyData $fbData, array $objects)
                         break;
 
                     case 'VFREEBUSY':
+                        /** @var VFreeBusy $component */
                         foreach ($component->FREEBUSY as $freebusy) {
                             $fbType = isset($freebusy['FBTYPE']) ? strtoupper($freebusy['FBTYPE']) : 'BUSY';
 
@@ -491,11 +473,12 @@ protected function calculateBusy(FreeBusyData $fbData, array $objects)
      * This method takes a FreeBusyData object and generates the VCALENDAR
      * object associated with it.
      *
-     * @return VCalendar
+     * @throws InvalidDataException
+     * @throws \Exception
      */
-    protected function generateFreeBusyCalendar(FreeBusyData $fbData)
+    protected function generateFreeBusyCalendar(FreeBusyData $fbData): VCalendar
     {
-        if ($this->baseObject) {
+        if (null !== $this->baseObject) {
             $calendar = $this->baseObject;
         } else {
             $calendar = new VCalendar();
@@ -505,19 +488,22 @@ protected function generateFreeBusyCalendar(FreeBusyData $fbData)
         $calendar->add($vfreebusy);
 
         if ($this->start) {
+            /** @var DateTime $dtstart */
             $dtstart = $calendar->createProperty('DTSTART');
             $dtstart->setDateTime($this->start);
             $vfreebusy->add($dtstart);
         }
         if ($this->end) {
+            /** @var DateTime $dtend */
             $dtend = $calendar->createProperty('DTEND');
             $dtend->setDateTime($this->end);
             $vfreebusy->add($dtend);
         }
 
         $tz = new \DateTimeZone('UTC');
+        /** @var DateTime $dtstamp */
         $dtstamp = $calendar->createProperty('DTSTAMP');
-        $dtstamp->setDateTime(new DateTimeImmutable('now', $tz));
+        $dtstamp->setDateTime(new \DateTimeImmutable('now', $tz));
         $vfreebusy->add($dtstamp);
 
         foreach ($fbData->getData() as $busyTime) {
diff --git a/lib/ITip/Broker.php b/lib/ITip/Broker.php
index b66a59f54..f792fd990 100644
--- a/lib/ITip/Broker.php
+++ b/lib/ITip/Broker.php
@@ -3,9 +3,14 @@
 namespace Sabre\VObject\ITip;
 
 use Sabre\VObject\Component\VCalendar;
+use Sabre\VObject\Component\VEvent;
 use Sabre\VObject\DateTimeParser;
+use Sabre\VObject\InvalidDataException;
+use Sabre\VObject\ParseException;
 use Sabre\VObject\Reader;
 use Sabre\VObject\Recur\EventIterator;
+use Sabre\VObject\Recur\MaxInstancesExceededException;
+use Sabre\VObject\Recur\NoInstancesException;
 
 /**
  * The ITip\Broker class is a utility class that helps with processing
@@ -13,7 +18,7 @@
  *
  * iTip is defined in rfc5546, stands for iCalendar Transport-Independent
  * Interoperability Protocol, and describes the underlying mechanism for
- * using iCalendar for scheduling for for example through email (also known as
+ * using iCalendar for scheduling, for example, through email (also known as
  * IMip) and CalDAV Scheduling.
  *
  * This class helps by:
@@ -27,7 +32,7 @@
  *    a received invite.
  * 4. It can also process an invite update on a local event, ensuring that any
  *    overridden properties from attendees are retained.
- * 5. It can create a accepted or declined iTip reply based on an invite.
+ * 5. It can create an accepted or declined iTip reply based on an invite.
  * 6. It can process a reply from an invite and update an events attendee
  *     status based on a reply.
  *
@@ -49,10 +54,8 @@ class Broker
      * CLIENT will be ignored. This is the desired behavior for a CalDAV
      * server, but if you're writing an iTip application that doesn't deal with
      * CalDAV, you may want to ignore this parameter.
-     *
-     * @var bool
      */
-    public $scheduleAgentServerRules = true;
+    public bool $scheduleAgentServerRules = true;
 
     /**
      * The broker will try during 'parseEvent' figure out whether the change
@@ -66,7 +69,7 @@ class Broker
      *
      * @var string[]
      */
-    public $significantChangeProperties = [
+    public array $significantChangeProperties = [
         'DTSTART',
         'DTEND',
         'DURATION',
@@ -104,9 +107,11 @@ class Broker
      *
      * If the iTip message was not supported, we will always return false.
      *
-     * @param VCalendar $existingObject
+     * @return VCalendar|false|void|null
      *
-     * @return VCalendar|null
+     * @throws InvalidDataException
+     * @throws MaxInstancesExceededException
+     * @throws NoInstancesException
      */
     public function processMessage(Message $itipMessage, VCalendar $existingObject = null)
     {
@@ -129,8 +134,6 @@ public function processMessage(Message $itipMessage, VCalendar $existingObject =
                 // Unsupported iTip message
                 return;
         }
-
-        return $existingObject;
     }
 
     /**
@@ -156,13 +159,16 @@ public function processMessage(Message $itipMessage, VCalendar $existingObject =
      * people. If the user was an attendee, we need to make sure that the
      * organizer gets the 'declined' message.
      *
-     * @param VCalendar|string $calendar
-     * @param string|array     $userHref
-     * @param VCalendar|string $oldCalendar
+     * @param VCalendar|string      $calendar
+     * @param string|array          $userHref
+     * @param VCalendar|string|null $oldCalendar
      *
-     * @return array
+     * @throws ITipException
+     * @throws InvalidDataException
+     * @throws ParseException
+     * @throws SameOrganizerForAllComponentsException
      */
-    public function parseEvent($calendar, $userHref, $oldCalendar = null)
+    public function parseEvent($calendar, $userHref, $oldCalendar = null): array
     {
         if ($oldCalendar) {
             if (is_string($oldCalendar)) {
@@ -216,7 +222,7 @@ public function parseEvent($calendar, $userHref, $oldCalendar = null)
             // The calendar object got deleted, we need to process this as a
             // cancellation / decline.
             if (!$oldCalendar) {
-                // No old and no new calendar, there's no thing to do.
+                // No old and no new calendar, there's nothing to do.
                 return [];
             }
 
@@ -261,20 +267,13 @@ public function parseEvent($calendar, $userHref, $oldCalendar = null)
      *
      * This is message from an organizer, and is either a new event
      * invite, or an update to an existing one.
-     *
-     * @param VCalendar $existingObject
-     *
-     * @return VCalendar|null
      */
-    protected function processMessageRequest(Message $itipMessage, VCalendar $existingObject = null)
+    protected function processMessageRequest(Message $itipMessage, VCalendar $existingObject = null): ?VCalendar
     {
         if (!$existingObject) {
             // This is a new invite, and we're just going to copy over
             // all the components from the invite.
             $existingObject = new VCalendar();
-            foreach ($itipMessage->message->getComponents() as $component) {
-                $existingObject->add(clone $component);
-            }
         } else {
             // We need to update an existing object with all the new
             // information. We can just remove all existing components
@@ -282,9 +281,9 @@ protected function processMessageRequest(Message $itipMessage, VCalendar $existi
             foreach ($existingObject->getComponents() as $component) {
                 $existingObject->remove($component);
             }
-            foreach ($itipMessage->message->getComponents() as $component) {
-                $existingObject->add(clone $component);
-            }
+        }
+        foreach ($itipMessage->message->getComponents() as $component) {
+            $existingObject->add(clone $component);
         }
 
         return $existingObject;
@@ -296,12 +295,8 @@ protected function processMessageRequest(Message $itipMessage, VCalendar $existi
      * This is a message from an organizer, and means that either an
      * attendee got removed from an event, or an event got cancelled
      * altogether.
-     *
-     * @param VCalendar $existingObject
-     *
-     * @return VCalendar|null
      */
-    protected function processMessageCancel(Message $itipMessage, VCalendar $existingObject = null)
+    protected function processMessageCancel(Message $itipMessage, VCalendar $existingObject = null): ?VCalendar
     {
         if (!$existingObject) {
             // The event didn't exist in the first place, so we're just
@@ -322,16 +317,16 @@ protected function processMessageCancel(Message $itipMessage, VCalendar $existin
      * The message is a reply. This is for example an attendee telling
      * an organizer he accepted the invite, or declined it.
      *
-     * @param VCalendar $existingObject
-     *
-     * @return VCalendar|null
+     * @throws InvalidDataException
+     * @throws MaxInstancesExceededException
+     * @throws NoInstancesException
      */
-    protected function processMessageReply(Message $itipMessage, VCalendar $existingObject = null)
+    protected function processMessageReply(Message $itipMessage, VCalendar $existingObject = null): ?VCalendar
     {
         // A reply can only be processed based on an existing object.
         // If the object is not available, the reply is ignored.
         if (!$existingObject) {
-            return;
+            return null;
         }
         $instances = [];
         $requestStatus = '2.0';
@@ -386,7 +381,7 @@ protected function processMessageReply(Message $itipMessage, VCalendar $existing
 
         if (!$masterObject) {
             // No master object, we can't add new instances.
-            return;
+            return null;
         }
         // If we got replies to instances that did not exist in the
         // original list, it means that new exceptions must be created.
@@ -446,10 +441,8 @@ protected function processMessageReply(Message $itipMessage, VCalendar $existing
      *
      * We will detect which attendees got added, which got removed and create
      * specific messages for these situations.
-     *
-     * @return array
      */
-    protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo, array $oldEventInfo)
+    protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo, array $oldEventInfo): array
     {
         // Merging attendee lists.
         $attendees = [];
@@ -511,6 +504,7 @@ protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo,
 
                 $icalMsg->METHOD = $message->method;
 
+                /** @var VEvent $event */
                 $event = $icalMsg->add('VEVENT', [
                     'UID' => $message->uid,
                     'SEQUENCE' => $message->sequence,
@@ -551,10 +545,10 @@ protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo,
                 $newAttendeeInstances = array_keys($attendee['newInstances']);
 
                 $message->significantChange =
-                    'REQUEST' === $attendee['forceSend'] ||
-                    count($oldAttendeeInstances) != count($newAttendeeInstances) ||
-                    count(array_diff($oldAttendeeInstances, $newAttendeeInstances)) > 0 ||
-                    $oldEventInfo['significantChangeHash'] !== $eventInfo['significantChangeHash'];
+                    'REQUEST' === $attendee['forceSend']
+                    || count($oldAttendeeInstances) != count($newAttendeeInstances)
+                    || count(array_diff($oldAttendeeInstances, $newAttendeeInstances)) > 0
+                    || $oldEventInfo['significantChangeHash'] !== $eventInfo['significantChangeHash'];
 
                 foreach ($attendee['newInstances'] as $instanceId => $instanceInfo) {
                     $currentEvent = clone $eventInfo['instances'][$instanceId];
@@ -615,11 +609,11 @@ protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo,
      *
      * This function figures out if we need to send a reply to an organizer.
      *
-     * @param string $attendee
-     *
      * @return Message[]
+     *
+     * @throws InvalidDataException
      */
-    protected function parseEventForAttendee(VCalendar $calendar, array $eventInfo, array $oldEventInfo, $attendee)
+    protected function parseEventForAttendee(VCalendar $calendar, array $eventInfo, array $oldEventInfo, string $attendee): array
     {
         if ($this->scheduleAgentServerRules && 'CLIENT' === $eventInfo['organizerScheduleAgent']) {
             return [];
@@ -710,6 +704,7 @@ protected function parseEventForAttendee(VCalendar $calendar, array $eventInfo,
                 continue;
             }
 
+            /** @var VEvent $event */
             $event = $icalMsg->add('VEVENT', [
                 'UID' => $message->uid,
                 'SEQUENCE' => $message->sequence,
@@ -796,11 +791,10 @@ protected function parseEventForAttendee(VCalendar $calendar, array $eventInfo,
      * 11. significantChangeHash
      * 12. status
      *
-     * @param VCalendar $calendar
-     *
-     * @return array
+     * @throws ITipException
+     * @throws SameOrganizerForAllComponentsException
      */
-    protected function parseEventInfo(VCalendar $calendar = null)
+    protected function parseEventInfo(VCalendar $calendar): array
     {
         $uid = null;
         $organizer = null;
@@ -811,8 +805,6 @@ protected function parseEventInfo(VCalendar $calendar = null)
         $status = null;
         $organizerScheduleAgent = 'SERVER';
 
-        $significantChangeHash = '';
-
         // Now we need to collect a list of attendees, and which instances they
         // are a part of.
         $attendees = [];
@@ -841,7 +833,7 @@ protected function parseEventInfo(VCalendar $calendar = null)
             if (isset($vevent->ORGANIZER)) {
                 if (is_null($organizer)) {
                     $organizer = $vevent->ORGANIZER->getNormalizedValue();
-                    $organizerName = isset($vevent->ORGANIZER['CN']) ? $vevent->ORGANIZER['CN'] : null;
+                    $organizerName = $vevent->ORGANIZER['CN'] ?? null;
                 } else {
                     if (strtoupper($organizer) !== strtoupper($vevent->ORGANIZER->getNormalizedValue())) {
                         throw new SameOrganizerForAllComponentsException('Every instance of the event must have the same organizer.');
@@ -894,9 +886,9 @@ protected function parseEventInfo(VCalendar $calendar = null)
             }
             if (isset($vevent->ATTENDEE)) {
                 foreach ($vevent->ATTENDEE as $attendee) {
-                    if ($this->scheduleAgentServerRules &&
-                        isset($attendee['SCHEDULE-AGENT']) &&
-                        'CLIENT' === strtoupper($attendee['SCHEDULE-AGENT']->getValue())
+                    if ($this->scheduleAgentServerRules
+                        && isset($attendee['SCHEDULE-AGENT'])
+                        && 'CLIENT' === strtoupper($attendee['SCHEDULE-AGENT']->getValue())
                     ) {
                         continue;
                     }
@@ -955,9 +947,7 @@ protected function parseEventInfo(VCalendar $calendar = null)
 
         asort($significantChangeEventProperties);
 
-        foreach ($significantChangeEventProperties as $eventSignificantChangeHash) {
-            $significantChangeHash .= $eventSignificantChangeHash;
-        }
+        $significantChangeHash = implode('', $significantChangeEventProperties);
         $significantChangeHash = md5($significantChangeHash);
 
         return compact(
diff --git a/lib/ITip/ITipException.php b/lib/ITip/ITipException.php
index 949563614..c949cdb7c 100644
--- a/lib/ITip/ITipException.php
+++ b/lib/ITip/ITipException.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\ITip;
 
-use Exception;
-
 /**
  * This message is emitted in case of serious problems with iTip messages.
  *
@@ -11,6 +9,6 @@
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
  */
-class ITipException extends Exception
+class ITipException extends \Exception
 {
 }
diff --git a/lib/ITip/Message.php b/lib/ITip/Message.php
index 43536f172..9aa93996a 100644
--- a/lib/ITip/Message.php
+++ b/lib/ITip/Message.php
@@ -2,6 +2,8 @@
 
 namespace Sabre\VObject\ITip;
 
+use Sabre\VObject\Component\VCalendar;
+
 /**
  * This class represents an iTip message.
  *
@@ -18,32 +20,24 @@ class Message
 {
     /**
      * The object's UID.
-     *
-     * @var string
      */
-    public $uid;
+    public string $uid;
 
     /**
      * The component type, such as VEVENT.
-     *
-     * @var string
      */
-    public $component;
+    public string $component;
 
     /**
      * Contains the ITip method, which is something like REQUEST, REPLY or
      * CANCEL.
-     *
-     * @var string
      */
-    public $method;
+    public ?string $method;
 
     /**
      * The current sequence number for the event.
-     *
-     * @var int
      */
-    public $sequence;
+    public ?int $sequence;
 
     /**
      * The senders' email address.
@@ -51,33 +45,25 @@ class Message
      * Note that this does not imply that this has to be used in a From: field
      * if the message is sent by email. It may also be populated in Reply-To:
      * or not at all.
-     *
-     * @var string
      */
-    public $sender;
+    public string $sender;
 
     /**
      * The name of the sender. This is often populated from a CN parameter from
      * either the ORGANIZER or ATTENDEE, depending on the message.
-     *
-     * @var string|null
      */
-    public $senderName;
+    public ?string $senderName;
 
     /**
      * The recipient's email address.
-     *
-     * @var string
      */
-    public $recipient;
+    public string $recipient;
 
     /**
      * The name of the recipient. This is usually populated with the CN
      * parameter from the ATTENDEE or ORGANIZER property, if it's available.
-     *
-     * @var string|null
      */
-    public $recipientName;
+    public ?string $recipientName;
 
     /**
      * After the message has been delivered, this should contain a string such
@@ -87,17 +73,13 @@ class Message
      *
      * See:
      * http://tools.ietf.org/html/rfc6638#section-7.3
-     *
-     * @var string
      */
-    public $scheduleStatus;
+    public ?string $scheduleStatus = null;
 
     /**
      * The iCalendar / iTip body.
-     *
-     * @var \Sabre\VObject\Component\VCalendar
      */
-    public $message;
+    public VCalendar $message;
 
     /**
      * This will be set to true, if the iTip broker considers the change
@@ -110,10 +92,8 @@ class Message
      *
      * To see the list of properties that are considered 'significant', check
      * out Sabre\VObject\ITip\Broker::$significantChangeProperties.
-     *
-     * @var bool
      */
-    public $significantChange = true;
+    public bool $significantChange = true;
 
     /**
      * Returns the schedule status as a string.
diff --git a/lib/Node.php b/lib/Node.php
index 2041b2ac7..0dbe7cfad 100644
--- a/lib/Node.php
+++ b/lib/Node.php
@@ -19,7 +19,7 @@ abstract class Node implements \IteratorAggregate, \ArrayAccess, \Countable, \Js
      * If REPAIR is set, the validator will attempt to repair any broken data
      * (if possible).
      */
-    const REPAIR = 1;
+    public const REPAIR = 1;
 
     /**
      * If this option is set, the validator will operate on the vcards on the
@@ -28,7 +28,7 @@ abstract class Node implements \IteratorAggregate, \ArrayAccess, \Countable, \Js
      * This means for example that the UID is required, whereas it is not for
      * regular vcards.
      */
-    const PROFILE_CARDDAV = 2;
+    public const PROFILE_CARDDAV = 2;
 
     /**
      * If this option is set, the validator will operate on iCalendar objects
@@ -37,41 +37,33 @@ abstract class Node implements \IteratorAggregate, \ArrayAccess, \Countable, \Js
      * This means for example that calendars can only contain objects with
      * identical component types and UIDs.
      */
-    const PROFILE_CALDAV = 4;
+    public const PROFILE_CALDAV = 4;
 
     /**
      * Reference to the parent object, if this is not the top object.
-     *
-     * @var Node
      */
-    public $parent;
+    public ?Node $parent;
 
     /**
      * Iterator override.
-     *
-     * @var ElementList
      */
-    protected $iterator = null;
+    protected ?ElementList $iterator = null;
 
     /**
      * The root document.
-     *
-     * @var Component
      */
-    protected $root;
+    protected ?Component $root;
 
     /**
      * Serializes the node into a mimedir format.
-     *
-     * @return string
      */
-    abstract public function serialize();
+    abstract public function serialize(): string;
 
     /**
      * This method returns an array, with the representation as it should be
      * encoded in JSON. This is used to create jCard or jCal documents.
      *
-     * @return array
+     * @return array|string
      */
     #[\ReturnTypeWillChange]
     abstract public function jsonSerialize();
@@ -82,7 +74,7 @@ abstract public function jsonSerialize();
      *
      * @param Xml\Writer $writer XML writer
      */
-    abstract public function xmlSerialize(Xml\Writer $writer);
+    abstract public function xmlSerialize(Xml\Writer $writer): void;
 
     /**
      * Call this method on a document if you're done using it.
@@ -90,7 +82,7 @@ abstract public function xmlSerialize(Xml\Writer $writer);
      * It's intended to remove all circular references, so PHP can easily clean
      * it up.
      */
-    public function destroy()
+    public function destroy(): void
     {
         $this->parent = null;
         $this->root = null;
@@ -100,11 +92,9 @@ public function destroy()
 
     /**
      * Returns the iterator for this object.
-     *
-     * @return ElementList
      */
     #[\ReturnTypeWillChange]
-    public function getIterator()
+    public function getIterator(): ?ElementList
     {
         if (!is_null($this->iterator)) {
             return $this->iterator;
@@ -118,7 +108,7 @@ public function getIterator()
      *
      * Note that this is not actually part of the iterator interface
      */
-    public function setIterator(ElementList $iterator)
+    public function setIterator(ElementList $iterator): void
     {
         $this->iterator = $iterator;
     }
@@ -140,12 +130,8 @@ public function setIterator(ElementList $iterator)
      *   1 - The issue was repaired (only happens if REPAIR was turned on)
      *   2 - An inconsequential issue
      *   3 - A severe issue.
-     *
-     * @param int $options
-     *
-     * @return array
      */
-    public function validate($options = 0)
+    public function validate(int $options = 0): array
     {
         return [];
     }
@@ -156,11 +142,9 @@ public function validate($options = 0)
 
     /**
      * Returns the number of elements.
-     *
-     * @return int
      */
     #[\ReturnTypeWillChange]
-    public function count()
+    public function count(): int
     {
         $it = $this->getIterator();
 
@@ -177,11 +161,9 @@ public function count()
      * This method just forwards the request to the inner iterator
      *
      * @param int $offset
-     *
-     * @return bool
      */
     #[\ReturnTypeWillChange]
-    public function offsetExists($offset)
+    public function offsetExists($offset): bool
     {
         $iterator = $this->getIterator();
 
@@ -194,8 +176,6 @@ public function offsetExists($offset)
      * This method just forwards the request to the inner iterator
      *
      * @param int $offset
-     *
-     * @return mixed
      */
     #[\ReturnTypeWillChange]
     public function offsetGet($offset)
@@ -210,19 +190,18 @@ public function offsetGet($offset)
      *
      * This method just forwards the request to the inner iterator
      *
-     * @param int   $offset
-     * @param mixed $value
+     * @param int $offset
      */
     #[\ReturnTypeWillChange]
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         $iterator = $this->getIterator();
         $iterator->offsetSet($offset, $value);
 
         // @codeCoverageIgnoreStart
-    //
-    // This method always throws an exception, so we ignore the closing
-    // brace
+        //
+        // This method always throws an exception, so we ignore the closing
+        // brace
     }
 
     // @codeCoverageIgnoreEnd
@@ -235,15 +214,15 @@ public function offsetSet($offset, $value)
      * @param int $offset
      */
     #[\ReturnTypeWillChange]
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
         $iterator = $this->getIterator();
         $iterator->offsetUnset($offset);
 
         // @codeCoverageIgnoreStart
-    //
-    // This method always throws an exception, so we ignore the closing
-    // brace
+        //
+        // This method always throws an exception, so we ignore the closing
+        // brace
     }
 
     // @codeCoverageIgnoreEnd
diff --git a/lib/PHPUnitAssertions.php b/lib/PHPUnitAssertions.php
index 45c0a21c6..1976c3afd 100644
--- a/lib/PHPUnitAssertions.php
+++ b/lib/PHPUnitAssertions.php
@@ -30,9 +30,8 @@ trait PHPUnitAssertions
      *
      * @param resource|string|Component $expected
      * @param resource|string|Component $actual
-     * @param string                    $message
      */
-    public function assertVObjectEqualsVObject($expected, $actual, $message = '')
+    public function assertVObjectEqualsVObject($expected, $actual, string $message = ''): void
     {
         $getObj = function ($input) {
             if (is_resource($input)) {
diff --git a/lib/Parameter.php b/lib/Parameter.php
index 5df6238e0..1ef7da88a 100644
--- a/lib/Parameter.php
+++ b/lib/Parameter.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject;
 
-use ArrayIterator;
 use Sabre\Xml;
 
 /**
@@ -21,24 +20,20 @@ class Parameter extends Node
 {
     /**
      * Parameter name.
-     *
-     * @var string
      */
-    public $name;
+    public string $name;
 
     /**
      * vCard 2.1 allows parameters to be encoded without a name.
      *
      * We can deduce the parameter name based on its value.
-     *
-     * @var bool
      */
-    public $noName = false;
+    public bool $noName = false;
 
     /**
      * Parameter value.
      *
-     * @var string
+     * @var string|array|null
      */
     protected $value;
 
@@ -47,16 +42,17 @@ class Parameter extends Node
      *
      * It's recommended to use the create:: factory method instead.
      *
-     * @param string|null $name
-     * @param string $value
+     * @param string|array|null $value
      */
-    public function __construct(Document $root, $name, $value = null)
+    public function __construct(Document $root, ?string $name, $value = null)
     {
         $this->name = is_null($name) ? '' : strtoupper($name);
         $this->root = $root;
         if (is_null($name)) {
             $this->noName = true;
             $this->name = static::guessParameterNameByValue($value);
+        } else {
+            $this->name = strtoupper($name);
         }
 
         // If guessParameterNameByValue() returns an empty string
@@ -76,12 +72,8 @@ public function __construct(Document $root, $name, $value = null)
      * Figuring out what the name should have been. Note that a ton of
      * these are rather silly in 2014 and would probably rarely be
      * used, but we like to be complete.
-     *
-     * @param string $value
-     *
-     * @return string
      */
-    public static function guessParameterNameByValue($value)
+    public static function guessParameterNameByValue(string $value): string
     {
         switch (strtoupper($value)) {
             // Encodings
@@ -91,16 +83,16 @@ public static function guessParameterNameByValue($value)
                 $name = 'ENCODING';
                 break;
 
-            // Common types
+                // Common types
             case 'WORK':
             case 'HOME':
             case 'PREF':
-            // Delivery Label Type
+                // Delivery Label Type
             case 'DOM':
             case 'INTL':
             case 'POSTAL':
             case 'PARCEL':
-            // Telephone types
+                // Telephone types
             case 'VOICE':
             case 'FAX':
             case 'MSG':
@@ -111,7 +103,7 @@ public static function guessParameterNameByValue($value)
             case 'CAR':
             case 'ISDN':
             case 'VIDEO':
-            // EMAIL types (lol)
+                // EMAIL types (lol)
             case 'AOL':
             case 'APPLELINK':
             case 'ATTMAIL':
@@ -124,7 +116,7 @@ public static function guessParameterNameByValue($value)
             case 'PRODIGY':
             case 'TLX':
             case 'X400':
-            // Photo / Logo format types
+                // Photo / Logo format types
             case 'GIF':
             case 'CGM':
             case 'WMF':
@@ -139,17 +131,17 @@ public static function guessParameterNameByValue($value)
             case 'MPEG2':
             case 'AVI':
             case 'QTIME':
-            // Sound Digital Audio Type
+                // Sound Digital Audio Type
             case 'WAVE':
             case 'PCM':
             case 'AIFF':
-            // Key types
+                // Key types
             case 'X509':
             case 'PGP':
                 $name = 'TYPE';
                 break;
 
-            // Value types
+                // Value types
             case 'INLINE':
             case 'URL':
             case 'CONTENT-ID':
@@ -171,7 +163,7 @@ public static function guessParameterNameByValue($value)
      *
      * @param string|array $value
      */
-    public function setValue($value)
+    public function setValue($value): void
     {
         $this->value = $value;
     }
@@ -181,10 +173,8 @@ public function setValue($value)
      *
      * This method will always return a string, or null. If there were multiple
      * values, it will automatically concatenate them (separated by comma).
-     *
-     * @return string|null
      */
-    public function getValue()
+    public function getValue(): ?string
     {
         if (is_array($this->value)) {
             return implode(',', $this->value);
@@ -196,7 +186,7 @@ public function getValue()
     /**
      * Sets multiple values for this parameter.
      */
-    public function setParts(array $value)
+    public function setParts(array $value): void
     {
         $this->value = $value;
     }
@@ -205,10 +195,8 @@ public function setParts(array $value)
      * Returns all values for this parameter.
      *
      * If there were no values, an empty array will be returned.
-     *
-     * @return array
      */
-    public function getParts()
+    public function getParts(): array
     {
         if (is_array($this->value)) {
             return $this->value;
@@ -227,7 +215,7 @@ public function getParts()
      *
      * @param string|array $part
      */
-    public function addValue($part)
+    public function addValue($part): void
     {
         if (is_null($this->value)) {
             $this->value = $part;
@@ -239,15 +227,11 @@ public function addValue($part)
     /**
      * Checks if this parameter contains the specified value.
      *
-     * This is a case-insensitive match. It makes sense to call this for for
-     * instance the TYPE parameter, to see if it contains a keyword such as
+     * This is a case-insensitive match. It makes sense to call this for
+     * the TYPE parameter, for instance, to see if it contains a keyword such as
      * 'WORK' or 'FAX'.
-     *
-     * @param string $value
-     *
-     * @return bool
      */
-    public function has($value)
+    public function has(string $value): bool
     {
         return in_array(
             strtolower($value),
@@ -257,10 +241,8 @@ public function has($value)
 
     /**
      * Turns the object back into a serialized blob.
-     *
-     * @return string
      */
-    public function serialize()
+    public function serialize(): string
     {
         $value = $this->getParts();
 
@@ -319,7 +301,7 @@ function ($out, $item) {
      * This method returns an array, with the representation as it should be
      * encoded in JSON. This is used to create jCard or jCal documents.
      *
-     * @return array
+     * @return array|string|null
      */
     #[\ReturnTypeWillChange]
     public function jsonSerialize()
@@ -333,7 +315,7 @@ public function jsonSerialize()
      *
      * @param Xml\Writer $writer XML writer
      */
-    public function xmlSerialize(Xml\Writer $writer)
+    public function xmlSerialize(Xml\Writer $writer): void
     {
         foreach (explode(',', $this->value) as $value) {
             $writer->writeElement('text', $value);
@@ -342,26 +324,22 @@ public function xmlSerialize(Xml\Writer $writer)
 
     /**
      * Called when this object is being cast to a string.
-     *
-     * @return string
      */
-    public function __toString()
+    public function __toString(): string
     {
         return (string) $this->getValue();
     }
 
     /**
      * Returns the iterator for this object.
-     *
-     * @return ElementList
      */
     #[\ReturnTypeWillChange]
-    public function getIterator()
+    public function getIterator(): ElementList
     {
         if (!is_null($this->iterator)) {
             return $this->iterator;
         }
 
-        return $this->iterator = new ArrayIterator((array) $this->value);
+        return $this->iterator = new ElementList((array) $this->value);
     }
 }
diff --git a/lib/Parser/Json.php b/lib/Parser/Json.php
index f33603207..df87114a1 100644
--- a/lib/Parser/Json.php
+++ b/lib/Parser/Json.php
@@ -2,11 +2,14 @@
 
 namespace Sabre\VObject\Parser;
 
+use Sabre\VObject\Component;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Component\VCard;
 use Sabre\VObject\Document;
 use Sabre\VObject\EofException;
+use Sabre\VObject\InvalidDataException;
 use Sabre\VObject\ParseException;
+use Sabre\VObject\Property;
 use Sabre\VObject\Property\FlatText;
 use Sabre\VObject\Property\Text;
 
@@ -23,17 +26,13 @@ class Json extends Parser
 {
     /**
      * The input data.
-     *
-     * @var array
      */
-    protected $input;
+    protected ?array $input;
 
     /**
      * Root component.
-     *
-     * @var Document
      */
-    protected $root;
+    protected ?Document $root;
 
     /**
      * This method starts the parsing process.
@@ -44,11 +43,12 @@ class Json extends Parser
      * If either input or options are not supplied, the defaults will be used.
      *
      * @param resource|string|array|null $input
-     * @param int                        $options
      *
-     * @return \Sabre\VObject\Document
+     * @throws EofException
+     * @throws ParseException
+     * @throws InvalidDataException
      */
-    public function parse($input = null, $options = 0)
+    public function parse($input = null, int $options = 0): ?Document
     {
         if (!is_null($input)) {
             $this->setInput($input);
@@ -80,7 +80,7 @@ public function parse($input = null, $options = 0)
             }
         }
 
-        // Resetting the input so we can throw an feof exception the next time.
+        // Resetting the input so that we can throw an feof exception the next time.
         $this->input = null;
 
         return $this->root;
@@ -89,9 +89,9 @@ public function parse($input = null, $options = 0)
     /**
      * Parses a component.
      *
-     * @return \Sabre\VObject\Component
+     * @throws InvalidDataException
      */
-    public function parseComponent(array $jComp)
+    public function parseComponent(array $jComp): Component
     {
         // We can remove $self from PHP 5.4 onward.
         $self = $this;
@@ -117,16 +117,16 @@ function ($jComp) use ($self) {
         return $this->root->createComponent(
             $jComp[0],
             array_merge($properties, $components),
-            $defaults = false
+            false
         );
     }
 
     /**
      * Parses properties.
      *
-     * @return \Sabre\VObject\Property
+     * @throws InvalidDataException
      */
-    public function parseProperty(array $jProp)
+    public function parseProperty(array $jProp): Property
     {
         list(
             $propertyName,
@@ -177,7 +177,7 @@ public function parseProperty(array $jProp)
      *
      * @param resource|string|array $input
      */
-    public function setInput($input)
+    public function setInput($input): void
     {
         if (is_resource($input)) {
             $input = stream_get_contents($input);
diff --git a/lib/Parser/MimeDir.php b/lib/Parser/MimeDir.php
index b0b52d223..1ba2f1c59 100644
--- a/lib/Parser/MimeDir.php
+++ b/lib/Parser/MimeDir.php
@@ -2,13 +2,14 @@
 
 namespace Sabre\VObject\Parser;
 
-use Sabre\VObject\Component;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Component\VCard;
 use Sabre\VObject\Document;
 use Sabre\VObject\EofException;
+use Sabre\VObject\InvalidDataException;
 use Sabre\VObject\Node;
 use Sabre\VObject\ParseException;
+use Sabre\VObject\Property;
 use Sabre\VObject\Reader;
 
 /**
@@ -35,13 +36,11 @@ class MimeDir extends Parser
 
     /**
      * Root component.
-     *
-     * @var Component
      */
-    protected $root;
+    protected ?Document $root;
 
     /**
-     * By default all input will be assumed to be UTF-8.
+     * By default, all input will be assumed to be UTF-8.
      *
      * However, both iCalendar and vCard might be encoded using different
      * character sets. The character set is usually set in the mime-type.
@@ -49,17 +48,15 @@ class MimeDir extends Parser
      * If this is the case, use setEncoding to specify that a different
      * encoding will be used. If this is set, the parser will automatically
      * convert all incoming data to UTF-8.
-     *
-     * @var string
      */
-    protected $charset = 'UTF-8';
+    protected string $charset = 'UTF-8';
 
     /**
      * The list of character sets we support when decoding.
      *
      * This would be a const expression but for now we need to support PHP 5.5
      */
-    protected static $SUPPORTED_CHARSETS = [
+    protected static array $SUPPORTED_CHARSETS = [
         'UTF-8',
         'ISO-8859-1',
         'Windows-1252',
@@ -72,15 +69,14 @@ class MimeDir extends Parser
      * used.
      *
      * @param string|resource|null $input
-     * @param int                  $options
      *
-     * @return \Sabre\VObject\Document
+     * @throws ParseException
      */
-    public function parse($input = null, $options = 0)
+    public function parse($input = null, int $options = 0): ?Document
     {
         $this->root = null;
 
-        if (!is_null($input)) {
+        if (!\is_null($input)) {
             $this->setInput($input);
         }
 
@@ -94,7 +90,7 @@ public function parse($input = null, $options = 0)
     }
 
     /**
-     * By default all input will be assumed to be UTF-8.
+     * By default, all input will be assumed to be UTF-8.
      *
      * However, both iCalendar and vCard might be encoded using different
      * character sets. The character set is usually set in the mime-type.
@@ -102,10 +98,8 @@ public function parse($input = null, $options = 0)
      * If this is the case, use setEncoding to specify that a different
      * encoding will be used. If this is set, the parser will automatically
      * convert all incoming data to UTF-8.
-     *
-     * @param string $charset
      */
-    public function setCharset($charset)
+    public function setCharset(string $charset): void
     {
         if (!in_array($charset, self::$SUPPORTED_CHARSETS)) {
             throw new \InvalidArgumentException('Unsupported encoding. (Supported encodings: '.implode(', ', self::$SUPPORTED_CHARSETS).')');
@@ -117,6 +111,8 @@ public function setCharset($charset)
      * Sets the input buffer. Must be a string or stream.
      *
      * @param resource|string $input
+     *
+     * @return void
      */
     public function setInput($input)
     {
@@ -139,18 +135,21 @@ public function setInput($input)
 
     /**
      * Parses an entire document.
+     *
+     * @throws EofException
+     * @throws ParseException
      */
-    protected function parseDocument()
+    protected function parseDocument(): void
     {
         $line = $this->readLine();
 
         // BOM is ZERO WIDTH NO-BREAK SPACE (U+FEFF).
         // It's 0xEF 0xBB 0xBF in UTF-8 hex.
         if (3 <= strlen($line)
-            && 0xef === ord($line[0])
-            && 0xbb === ord($line[1])
-            && 0xbf === ord($line[2])) {
-            $line = substr($line, 3);
+            && 0xEF === ord($line[0])
+            && 0xBB === ord($line[1])
+            && 0xBF === ord($line[2])) {
+            $line = \substr($line, 3);
         }
 
         switch (strtoupper($line)) {
@@ -168,8 +167,12 @@ protected function parseDocument()
 
         while (true) {
             // Reading until we hit END:
-            $line = $this->readLine();
-            if ('END:' === strtoupper(substr($line, 0, 4))) {
+            try {
+                $line = $this->readLine();
+            } catch (EofException $oEx) {
+                $line = 'END:'.$this->root->name;
+            }
+            if ('END:' === strtoupper(\substr($line, 0, 4))) {
                 break;
             }
             $result = $this->parseLine($line);
@@ -178,7 +181,7 @@ protected function parseDocument()
             }
         }
 
-        $name = strtoupper(substr($line, 4));
+        $name = strtoupper(\substr($line, 4));
         if ($name !== $this->root->name) {
             throw new ParseException('Invalid MimeDir file. expected: "END:'.$this->root->name.'" got: "END:'.$name.'"');
         }
@@ -190,22 +193,25 @@ protected function parseDocument()
      *
      * @param string $line Unfolded line
      *
-     * @return Node
+     * @return Node|Property|false
+     *
+     * @throws EofException
+     * @throws ParseException
      */
-    protected function parseLine($line)
+    protected function parseLine(string $line)
     {
         // Start of a new component
-        if ('BEGIN:' === strtoupper(substr($line, 0, 6))) {
-            if (substr($line, 6) === $this->root->name) {
+        if ('BEGIN:' === strtoupper(\substr($line, 0, 6))) {
+            if (\substr($line, 6) === $this->root->name) {
                 throw new ParseException('Invalid MimeDir file. Unexpected component: "'.$line.'" in document type '.$this->root->name);
             }
-            $component = $this->root->createComponent(substr($line, 6), [], false);
+            $component = $this->root->createComponent(\substr($line, 6), [], false);
 
             $prevNode = null;
             while (true) {
                 // Reading until we hit END:
                 $line = $this->readLine();
-                if ('END:' === strtoupper(substr($line, 0, 4))) {
+                if ('END:' === strtoupper(\substr($line, 0, 4))) {
                     break;
                 }
                 try {
@@ -217,7 +223,7 @@ protected function parseLine($line)
                     ) {
                         // Fix unfolding
                         $component->remove($prevNode);
-                        $value = $prevNode->getValue() . ' ' . $line . PHP_EOL;
+                        $value = $prevNode->getValue().' '.$line.PHP_EOL;
                         $prevNode->offsetSet('VALUE', $value);
                         $prevNode->setValue($value);
                         $component->add($prevNode);
@@ -230,7 +236,7 @@ protected function parseLine($line)
                 }
             }
 
-            $name = strtoupper(substr($line, 4));
+            $name = strtoupper(\substr($line, 4));
             if ($name !== $component->name) {
                 throw new ParseException('Invalid MimeDir file. expected: "END:'.$component->name.'" got: "END:'.$name.'"');
             }
@@ -253,41 +259,33 @@ protected function parseLine($line)
      * the next line.
      *
      * If that was not the case, we store it here.
-     *
-     * @var string|null
      */
-    protected $lineBuffer;
+    protected ?string $lineBuffer = null;
 
     /**
      * The real current line number.
      */
-    protected $lineIndex = 0;
+    protected int $lineIndex = 0;
 
     /**
      * In the case of unfolded lines, this property holds the line number for
      * the start of the line.
-     *
-     * @var int
      */
-    protected $startLine = 0;
+    protected int $startLine = 0;
 
     /**
      * Contains a 'raw' representation of the current line.
-     *
-     * @var string
      */
-    protected $rawLine;
+    protected string $rawLine;
 
     /**
      * Reads a single line from the buffer.
      *
      * This method strips any newlines and also takes care of unfolding.
      *
-     * @throws \Sabre\VObject\EofException
-     *
-     * @return string
+     * @throws EofException|ParseException
      */
-    protected function readLine()
+    protected function readLine(): ?string
     {
         if (!\is_null($this->lineBuffer)) {
             $rawLine = $this->lineBuffer;
@@ -335,8 +333,12 @@ protected function readLine()
 
     /**
      * Reads a property or component from a line.
+     *
+     * @return Property|false
+     *
+     * @throws ParseException|InvalidDataException
      */
-    protected function readProperty($line)
+    protected function readProperty(string $line)
     {
         if ($this->options & self::OPTION_FORGIVING) {
             $propNameToken = 'A-Z0-9\-\._\\/';
@@ -361,7 +363,7 @@ protected function readProperty($line)
             ) (?=[;:,])
             /xi";
 
-        //echo $regex, "\n"; exit();
+        // echo $regex, "\n"; exit();
         preg_match_all($regex, $line, $matches, PREG_SET_ORDER);
 
         $property = [
@@ -382,21 +384,31 @@ protected function readProperty($line)
         foreach ($matches as $match) {
             if (isset($match['paramValue'])) {
                 if ($match['paramValue'] && '"' === $match['paramValue'][0]) {
-                    $value = substr($match['paramValue'], 1, -1);
+                    $value = \substr($match['paramValue'], 1, -1);
                 } else {
                     $value = $match['paramValue'];
                 }
 
                 $value = $this->unescapeParam($value);
 
-                if (is_null($lastParam)) {
+                if (\is_null($lastParam)) {
+                    if ($this->options & self::OPTION_IGNORE_INVALID_LINES) {
+                        // When the property can't be matched and the configuration
+                        // option is set to ignore invalid lines, we ignore this line
+                        // This can happen when servers provide faulty data as iCloud
+                        //  frequently does with X-APPLE-STRUCTURED-LOCATION
+                        continue;
+                    }
                     throw new ParseException('Invalid Mimedir file. Line starting at '.$this->startLine.' did not follow iCalendar/vCard conventions');
                 }
-                if (is_null($property['parameters'][$lastParam])) {
+                if (\is_null($property['parameters'][$lastParam])) {
                     $property['parameters'][$lastParam] = $value;
                 } elseif (is_array($property['parameters'][$lastParam])) {
                     $property['parameters'][$lastParam][] = $value;
-                } elseif ($property['parameters'][$lastParam] !== $value) {
+                } elseif ($property['parameters'][$lastParam] === $value) {
+                    // When the current value of the parameter is the same as the
+                    // new one, then we can leave the current parameter as it is.
+                } else {
                     $property['parameters'][$lastParam] = [
                         $property['parameters'][$lastParam],
                         $value,
@@ -425,7 +437,7 @@ protected function readProperty($line)
             // @codeCoverageIgnoreEnd
         }
 
-        if (is_null($property['value'])) {
+        if (\is_null($property['value'])) {
             $property['value'] = '';
         }
         if (!$property['name']) {
@@ -444,7 +456,7 @@ protected function readProperty($line)
         $namelessParameters = [];
 
         foreach ($property['parameters'] as $name => $value) {
-            if (!is_null($value)) {
+            if (!\is_null($value)) {
                 $namedParameters[$name] = $value;
             } else {
                 $namelessParameters[] = $name;
@@ -458,6 +470,7 @@ protected function readProperty($line)
         }
 
         if (isset($propObj['ENCODING']) && 'QUOTED-PRINTABLE' === strtoupper($propObj['ENCODING'])) {
+            /* @var Property\Text|Property\FlatText $propObj */
             $propObj->setQuotedPrintableValue($this->extractQuotedPrintableValue());
         } else {
             $charset = $this->charset;
@@ -468,10 +481,8 @@ protected function readProperty($line)
             switch (strtolower($charset)) {
                 case 'utf-8':
                     break;
-                case 'iso-8859-1':
-                    $property['value'] = utf8_encode($property['value']);
-                    break;
                 case 'windows-1252':
+                case 'iso-8859-1':
                     $property['value'] = mb_convert_encoding($property['value'], 'UTF-8', $charset);
                     break;
                 default:
@@ -489,7 +500,7 @@ protected function readProperty($line)
      * vCard 2.1 says:
      *   * Semi-colons must be escaped in some property values, specifically
      *     ADR, ORG and N.
-     *   * Semi-colons must be escaped in parameter values, because semi-colons
+     *   * Semi-colons must be escaped in parameter values, because semicolons
      *     are also use to separate values.
      *   * No mention of escaping backslashes with another backslash.
      *   * newlines are not escaped either, instead QUOTED-PRINTABLE is used to
@@ -497,10 +508,10 @@ protected function readProperty($line)
      *
      * vCard 3.0 says:
      *   * (rfc2425) Backslashes, newlines (\n or \N) and comma's must be
-     *     escaped, all time time.
-     *   * Comma's are used for delimiters in multiple values
-     *   * (rfc2426) Adds to to this that the semi-colon MUST also be escaped,
-     *     as in some properties semi-colon is used for separators.
+     *     escaped, all the time.
+     *   * Commas are used for delimiters in multiple values
+     *   * (rfc2426) Adds to this that the semicolon MUST also be escaped,
+     *     as in some properties semicolon is used for separators.
      *   * Properties using semi-colons: N, ADR, GEO, ORG
      *   * Both ADR and N's individual parts may be broken up further with a
      *     comma.
@@ -508,12 +519,12 @@ protected function readProperty($line)
      *
      * vCard 4.0 (rfc6350) says:
      *   * Commas must be escaped.
-     *   * Semi-colons may be escaped, an unescaped semi-colon _may_ be a
+     *   * Semi-colons may be escaped, an unescaped semicolon _may_ be a
      *     delimiter, depending on the property.
      *   * Backslashes must be escaped
      *   * Newlines must be escaped as either \N or \n.
      *   * Some compound properties may contain multiple parts themselves, so a
-     *     comma within a semi-colon delimited property may also be unescaped
+     *     comma within a semicolon delimited property may also be unescaped
      *     to denote multiple parts _within_ the compound property.
      *   * Text-properties using semi-colons: N, ADR, ORG, CLIENTPIDMAP.
      *   * Text-properties using commas: NICKNAME, RELATED, CATEGORIES, PID.
@@ -522,7 +533,7 @@ protected function readProperty($line)
      * example for GEO in Section 6.5.2 seems to violate this.
      *
      * iCalendar 2.0 (rfc5545) says:
-     *   * Commas or semi-colons may be used as delimiters, depending on the
+     *   * Commas or semicolons may be used as delimiters, depending on the
      *     property.
      *   * Commas, semi-colons, backslashes, newline (\N or \n) are always
      *     escaped, unless they are delimiters.
@@ -532,20 +543,17 @@ protected function readProperty($line)
      *     insignificant.
      *   * Semi-colons are described as the delimiter for 'structured values'.
      *     They are specifically used in Semi-colons are used as a delimiter in
-     *     REQUEST-STATUS, RRULE, GEO and EXRULE. EXRULE is deprecated however.
+     *     REQUEST-STATUS, RRULE, GEO and EXRULE. EXRULE is deprecated, however.
      *
      * Now for the parameters
      *
      * If delimiter is not set (empty string) this method will just return a string.
-     * If it's a comma or a semi-colon the string will be split on those
+     * If it's a comma or a semicolon the string will be split on those
      * characters, and always return an array.
      *
-     * @param string $input
-     * @param string $delimiter
-     *
      * @return string|string[]
      */
-    public static function unescapeValue($input, $delimiter = ';')
+    public static function unescapeValue(string $input, string $delimiter = ';')
     {
         $regex = '#  (?: (\\\\ (?: \\\\ | N | n | ; | , ) )';
         if ($delimiter) {
@@ -595,11 +603,11 @@ public static function unescapeValue($input, $delimiter = ';')
      *   * Does not mention a mechanism for this. In addition, double quotes
      *     are never used to wrap values.
      *   * This means that parameters can simply not contain colons or
-     *     semi-colons.
+     *     semicolons.
      *
      * vCard 3.0 (rfc2425, rfc2426):
      *   * Parameters _may_ be surrounded by double quotes.
-     *   * If this is not the case, semi-colon, colon and comma may simply not
+     *   * If this is not the case, semicolon, colon and comma may simply not
      *     occur (the comma used for multiple parameter values though).
      *   * If it is surrounded by double-quotes, it may simply not contain
      *     double-quotes.
@@ -617,10 +625,8 @@ public static function unescapeValue($input, $delimiter = ';')
      *   * New-line is encoded as ^n
      *   * ^ is encoded as ^^.
      *   * " is encoded as ^'
-     *
-     * @param string $input
      */
-    private function unescapeParam($input)
+    private function unescapeParam(string $input): ?string
     {
         return
             preg_replace_callback(
@@ -634,7 +640,7 @@ function ($matches) {
                         case '\'':
                             return '"';
 
-                    // @codeCoverageIgnoreStart
+                            // @codeCoverageIgnoreStart
                     }
                     // @codeCoverageIgnoreEnd
                 },
@@ -650,9 +656,10 @@ function ($matches) {
      *
      * This method does not do any decoding.
      *
-     * @return string
+     * @throws EofException
+     * @throws ParseException
      */
-    private function extractQuotedPrintableValue()
+    private function extractQuotedPrintableValue(): string
     {
         // We need to parse the raw line again to get the start of the value.
         //
@@ -672,11 +679,11 @@ private function extractQuotedPrintableValue()
         // like unfolding, but we keep the newline.
         $value = str_replace("\n ", "\n", $value);
 
-        // Microsoft products don't always correctly fold lines, they may be
+        // Microsoft's products don't always correctly fold lines, they may be
         // missing a whitespace. So if 'forgiving' is turned on, we will take
         // those as well.
         if ($this->options & self::OPTION_FORGIVING) {
-            while ('=' === substr($value, -1) && $this->lineBuffer) {
+            while ('=' === \substr($value, -1) && $this->lineBuffer) {
                 // Reading the line
                 $this->readLine();
                 // Grabbing the raw form
diff --git a/lib/Parser/Parser.php b/lib/Parser/Parser.php
index b7b611430..29921d182 100644
--- a/lib/Parser/Parser.php
+++ b/lib/Parser/Parser.php
@@ -2,6 +2,8 @@
 
 namespace Sabre\VObject\Parser;
 
+use Sabre\VObject\Document;
+
 /**
  * Abstract parser.
  *
@@ -20,30 +22,27 @@ abstract class Parser
      * accept slashes and underscores in property names, and it will also
      * attempt to fix Microsoft vCard 2.1's broken line folding.
      */
-    const OPTION_FORGIVING = 1;
+    public const OPTION_FORGIVING = 1;
 
     /**
      * If this option is turned on, any lines we cannot parse will be ignored
      * by the reader.
      */
-    const OPTION_IGNORE_INVALID_LINES = 2;
+    public const OPTION_IGNORE_INVALID_LINES = 2;
 
     /**
      * Bitmask of parser options.
-     *
-     * @var int
      */
-    protected $options;
+    protected int $options;
 
     /**
      * Creates the parser.
      *
      * Optionally, it's possible to parse the input stream here.
      *
-     * @param mixed $input
-     * @param int   $options any parser options (OPTION constants)
+     * @param int $options any parser options (OPTION constants)
      */
-    public function __construct($input = null, $options = 0)
+    public function __construct($input = null, int $options = 0)
     {
         if (!is_null($input)) {
             $this->setInput($input);
@@ -59,17 +58,14 @@ public function __construct($input = null, $options = 0)
      *
      * If either input or options are not supplied, the defaults will be used.
      *
-     * @param mixed $input
-     * @param int   $options
-     *
-     * @return array
+     * @param resource|string|array|null $input
      */
-    abstract public function parse($input = null, $options = 0);
+    abstract public function parse($input = null, int $options = 0): ?Document;
 
     /**
      * Sets the input data.
      *
-     * @param mixed $input
+     * @param resource|string|array $input
      */
     abstract public function setInput($input);
 }
diff --git a/lib/Parser/XML.php b/lib/Parser/XML.php
index 78773173d..9a5100684 100644
--- a/lib/Parser/XML.php
+++ b/lib/Parser/XML.php
@@ -5,7 +5,9 @@
 use Sabre\VObject\Component;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Component\VCard;
+use Sabre\VObject\Document;
 use Sabre\VObject\EofException;
+use Sabre\VObject\InvalidDataException;
 use Sabre\VObject\ParseException;
 use Sabre\Xml as SabreXml;
 
@@ -20,39 +22,32 @@
  */
 class XML extends Parser
 {
-    const XCAL_NAMESPACE = 'urn:ietf:params:xml:ns:icalendar-2.0';
-    const XCARD_NAMESPACE = 'urn:ietf:params:xml:ns:vcard-4.0';
+    public const XCAL_NAMESPACE = 'urn:ietf:params:xml:ns:icalendar-2.0';
+    public const XCARD_NAMESPACE = 'urn:ietf:params:xml:ns:vcard-4.0';
 
     /**
      * The input data.
-     *
-     * @var array
      */
-    protected $input;
+    protected ?array $input;
 
     /**
      * A pointer/reference to the input.
-     *
-     * @var array
      */
-    private $pointer;
+    private ?array $pointer;
 
     /**
      * Document, root component.
-     *
-     * @var \Sabre\VObject\Document
      */
-    protected $root;
+    protected ?Document $root;
 
     /**
      * Creates the parser.
      *
      * Optionally, it's possible to parse the input stream here.
      *
-     * @param mixed $input
-     * @param int   $options any parser options (OPTION constants)
+     * @param int $options any parser options (OPTION constants)
      */
-    public function __construct($input = null, $options = 0)
+    public function __construct($input = null, int $options = 0)
     {
         if (0 === $options) {
             $options = parent::OPTION_FORGIVING;
@@ -64,14 +59,14 @@ public function __construct($input = null, $options = 0)
     /**
      * Parse xCal or xCard.
      *
-     * @param resource|string $input
-     * @param int             $options
+     * @param resource|string|null $input
      *
-     * @throws \Exception
-     *
-     * @return \Sabre\VObject\Document
+     * @throws EofException
+     * @throws InvalidDataException
+     * @throws ParseException
+     * @throws SabreXml\LibXMLException
      */
-    public function parse($input = null, $options = 0)
+    public function parse($input = null, int $options = 0): ?Document
     {
         if (!is_null($input)) {
             $this->setInput($input);
@@ -112,8 +107,10 @@ public function parse($input = null, $options = 0)
 
     /**
      * Parse a xCalendar component.
+     *
+     * @throws InvalidDataException
      */
-    protected function parseVCalendarComponents(Component $parentComponent)
+    protected function parseVCalendarComponents(Component $parentComponent): void
     {
         foreach ($this->pointer['value'] ?: [] as $children) {
             switch (static::getTagName($children['name'])) {
@@ -132,8 +129,10 @@ protected function parseVCalendarComponents(Component $parentComponent)
 
     /**
      * Parse a xCard component.
+     *
+     * @throws InvalidDataException
      */
-    protected function parseVCardComponents(Component $parentComponent)
+    protected function parseVCardComponents(Component $parentComponent): void
     {
         $this->pointer = &$this->pointer['value'];
         $this->parseProperties($parentComponent);
@@ -142,9 +141,9 @@ protected function parseVCardComponents(Component $parentComponent)
     /**
      * Parse xCalendar and xCard properties.
      *
-     * @param string $propertyNamePrefix
+     * @throws InvalidDataException
      */
-    protected function parseProperties(Component $parentComponent, $propertyNamePrefix = '')
+    protected function parseProperties(Component $parentComponent, string $propertyNamePrefix = ''): void
     {
         foreach ($this->pointer ?: [] as $xmlProperty) {
             list($namespace, $tagName) = SabreXml\Service::parseClarkNotation($xmlProperty['name']);
@@ -297,8 +296,10 @@ protected function parseProperties(Component $parentComponent, $propertyNamePref
 
     /**
      * Parse a component.
+     *
+     * @throws InvalidDataException
      */
-    protected function parseComponent(Component $parentComponent)
+    protected function parseComponent(Component $parentComponent): void
     {
         $components = $this->pointer['value'] ?: [];
 
@@ -320,12 +321,9 @@ protected function parseComponent(Component $parentComponent)
     /**
      * Create a property.
      *
-     * @param string $name
-     * @param array  $parameters
-     * @param string $type
-     * @param mixed  $value
+     * @throws InvalidDataException
      */
-    protected function createProperty(Component $parentComponent, $name, $parameters, $type, $value)
+    protected function createProperty(Component $parentComponent, string $name, array $parameters, string $type, $value): void
     {
         $property = $this->root->createProperty(
             $name,
@@ -340,9 +338,11 @@ protected function createProperty(Component $parentComponent, $name, $parameters
     /**
      * Sets the input data.
      *
-     * @param resource|string $input
+     * @param resource|string|array $input
+     *
+     * @throws SabreXml\LibXMLException
      */
-    public function setInput($input)
+    public function setInput($input): void
     {
         if (is_resource($input)) {
             $input = stream_get_contents($input);
@@ -363,12 +363,8 @@ public function setInput($input)
 
     /**
      * Get tag name from a Clark notation.
-     *
-     * @param string $clarkedTagName
-     *
-     * @return string
      */
-    protected static function getTagName($clarkedTagName)
+    protected static function getTagName(string $clarkedTagName): string
     {
         list(, $tagName) = SabreXml\Service::parseClarkNotation($clarkedTagName);
 
diff --git a/lib/Parser/XML/Element/KeyValue.php b/lib/Parser/XML/Element/KeyValue.php
index c0bbf0d9b..207f150b2 100644
--- a/lib/Parser/XML/Element/KeyValue.php
+++ b/lib/Parser/XML/Element/KeyValue.php
@@ -32,12 +32,8 @@ class KeyValue extends SabreXml\Element\KeyValue
      *
      * $reader->parseInnerTree() will parse the entire sub-tree, and advance to
      * the next element.
-     *
-     * @param XML\Reader $reader
-     *
-     * @return mixed
      */
-    public static function xmlDeserialize(SabreXml\Reader $reader)
+    public static function xmlDeserialize(SabreXml\Reader $reader): array
     {
         // If there's no children, we don't do anything.
         if ($reader->isEmptyElement) {
diff --git a/lib/Property.php b/lib/Property.php
index 56096dafe..53a252fb2 100644
--- a/lib/Property.php
+++ b/lib/Property.php
@@ -16,45 +16,40 @@
  */
 abstract class Property extends Node
 {
+    /**
+     * The root document.
+     */
+    public ?Component $root;
+
     /**
      * Property name.
      *
      * This will contain a string such as DTSTART, SUMMARY, FN.
-     *
-     * @var string
      */
-    public $name;
+    public ?string $name;
 
     /**
      * Property group.
      *
      * This is only used in vcards
-     *
-     * @var string|null
      */
-    public $group;
+    public ?string $group;
 
     /**
      * List of parameters.
-     *
-     * @var array
      */
-    public $parameters = [];
+    public array $parameters = [];
 
     /**
      * Current value.
-     *
-     * @var mixed
      */
     protected $value;
 
     /**
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
-     *
-     * @var string
      */
-    public $delimiter = ';';
+    public string $delimiter = ';';
 
     /**
      * Creates the generic property.
@@ -62,12 +57,11 @@ abstract class Property extends Node
      * Parameters must be specified in key=>value syntax.
      *
      * @param Component         $root       The root document
-     * @param string            $name
      * @param string|array|null $value
      * @param array             $parameters List of parameters
-     * @param string            $group      The vcard property group
+     * @param string|null       $group      The vcard property group
      */
-    public function __construct(Component $root, $name, $value = null, array $parameters = [], $group = null)
+    public function __construct(Component $root, ?string $name, $value = null, array $parameters = [], string $group = null)
     {
         $this->name = $name;
         $this->group = $group;
@@ -90,7 +84,7 @@ public function __construct(Component $root, $name, $value = null, array $parame
      *
      * @param string|array $value
      */
-    public function setValue($value)
+    public function setValue($value): void
     {
         $this->value = $value;
     }
@@ -103,28 +97,26 @@ public function setValue($value)
      * it as a string.
      *
      * To get the correct multi-value version, use getParts.
-     *
-     * @return string
      */
     public function getValue()
     {
         if (is_array($this->value)) {
             if (0 == count($this->value)) {
-                return;
+                return null;
             } elseif (1 === count($this->value)) {
                 return $this->value[0];
-            } else {
-                return $this->getRawMimeDirValue();
             }
-        } else {
-            return $this->value;
+
+            return $this->getRawMimeDirValue();
         }
+
+        return $this->value;
     }
 
     /**
      * Sets a multi-valued property.
      */
-    public function setParts(array $parts)
+    public function setParts(array $parts): void
     {
         $this->value = $parts;
     }
@@ -134,10 +126,8 @@ public function setParts(array $parts)
      *
      * This method always returns an array, if there was only a single value,
      * it will still be wrapped in an array.
-     *
-     * @return array
      */
-    public function getParts()
+    public function getParts(): array
     {
         if (is_null($this->value)) {
             return [];
@@ -155,10 +145,9 @@ public function getParts()
      * combined.
      * If nameless parameter is added, we try to guess its name.
      *
-     * @param string            $name
      * @param string|array|null $value
      */
-    public function add($name, $value = null)
+    public function add(?string $name, $value = null): void
     {
         $noName = false;
         if (null === $name) {
@@ -177,10 +166,8 @@ public function add($name, $value = null)
 
     /**
      * Returns an iterable list of children.
-     *
-     * @return array
      */
-    public function parameters()
+    public function parameters(): array
     {
         return $this->parameters;
     }
@@ -190,34 +177,26 @@ public function parameters()
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    abstract public function getValueType();
+    abstract public function getValueType(): string;
 
     /**
      * Sets a raw value coming from a mimedir (iCalendar/vCard) file.
      *
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
-     *
-     * @param string $val
      */
-    abstract public function setRawMimeDirValue($val);
+    abstract public function setRawMimeDirValue(string $val): void;
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    abstract public function getRawMimeDirValue();
+    abstract public function getRawMimeDirValue(): string;
 
     /**
      * Turns the object back into a serialized blob.
-     *
-     * @return string
      */
-    public function serialize()
+    public function serialize(): string
     {
         $str = $this->name;
         if ($this->group) {
@@ -248,10 +227,8 @@ public function serialize()
      * Returns the value, in the format it should be encoded for JSON.
      *
      * This method must always return an array.
-     *
-     * @return array
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         return $this->getParts();
     }
@@ -261,7 +238,7 @@ public function getJsonValue()
      *
      * The value must always be an array.
      */
-    public function setJsonValue(array $value)
+    public function setJsonValue(array $value): void
     {
         if (1 === count($value)) {
             $this->setValue(reset($value));
@@ -273,11 +250,9 @@ public function setJsonValue(array $value)
     /**
      * This method returns an array, with the representation as it should be
      * encoded in JSON. This is used to create jCard or jCal documents.
-     *
-     * @return array
      */
     #[\ReturnTypeWillChange]
-    public function jsonSerialize()
+    public function jsonSerialize(): array
     {
         $parameters = [];
 
@@ -304,10 +279,12 @@ public function jsonSerialize()
     }
 
     /**
-     * Hydrate data from a XML subtree, as it would appear in a xCard or xCal
+     * Hydrate data from an XML subtree, as it would appear in a xCard or xCal
      * object.
+     *
+     * @throws InvalidDataException
      */
-    public function setXmlValue(array $value)
+    public function setXmlValue(array $value): void
     {
         $this->setJsonValue($value);
     }
@@ -318,7 +295,7 @@ public function setXmlValue(array $value)
      *
      * @param Xml\Writer $writer XML writer
      */
-    public function xmlSerialize(Xml\Writer $writer)
+    public function xmlSerialize(Xml\Writer $writer): void
     {
         $parameters = [];
 
@@ -354,7 +331,7 @@ public function xmlSerialize(Xml\Writer $writer)
      *
      * @param Xml\Writer $writer XML writer
      */
-    protected function xmlSerializeValue(Xml\Writer $writer)
+    protected function xmlSerializeValue(Xml\Writer $writer): void
     {
         $valueType = strtolower($this->getValueType());
 
@@ -370,11 +347,9 @@ protected function xmlSerializeValue(Xml\Writer $writer)
      *
      * If the property only had a single value, you will get just that. In the
      * case the property had multiple values, the contents will be escaped and
-     * combined with ,.
-     *
-     * @return string
+     * combined with comma.
      */
-    public function __toString()
+    public function __toString(): string
     {
         return (string) $this->getValue();
     }
@@ -383,22 +358,18 @@ public function __toString()
 
     /**
      * Checks if an array element exists.
-     *
-     * @param mixed $name
-     *
-     * @return bool
      */
     #[\ReturnTypeWillChange]
-    public function offsetExists($name)
+    public function offsetExists($offset): bool
     {
-        if (is_int($name)) {
-            return parent::offsetExists($name);
+        if (is_int($offset)) {
+            return parent::offsetExists($offset);
         }
 
-        $name = strtoupper($name);
+        $offset = strtoupper($offset);
 
         foreach ($this->parameters as $parameter) {
-            if ($parameter->name == $name) {
+            if ($parameter->name == $offset) {
                 return true;
             }
         }
@@ -411,36 +382,34 @@ public function offsetExists($name)
      *
      * If the parameter does not exist, null is returned.
      *
-     * @param string $name
-     *
-     * @return Node
+     * @param string|int $offset
      */
     #[\ReturnTypeWillChange]
-    public function offsetGet($name)
+    public function offsetGet($offset): ?Node
     {
-        if (is_int($name)) {
-            return parent::offsetGet($name);
+        if (is_int($offset)) {
+            return parent::offsetGet($offset);
         }
-        $name = strtoupper($name);
+        $offset = strtoupper($offset);
 
-        if (!isset($this->parameters[$name])) {
-            return;
+        if (!isset($this->parameters[$offset])) {
+            return null;
         }
 
-        return $this->parameters[$name];
+        return $this->parameters[$offset];
     }
 
     /**
      * Creates a new parameter.
      *
-     * @param string $name
-     * @param mixed  $value
+     * @param string|int $offset
      */
     #[\ReturnTypeWillChange]
-    public function offsetSet($name, $value)
+    public function offsetSet($offset, $value): void
     {
-        if (is_int($name)) {
-            parent::offsetSet($name, $value);
+        if (is_int($offset)) {
+            parent::offsetSet($offset, $value);
+
             // @codeCoverageIgnoreStart
             // This will never be reached, because an exception is always
             // thrown.
@@ -448,20 +417,21 @@ public function offsetSet($name, $value)
             // @codeCoverageIgnoreEnd
         }
 
-        $param = new Parameter($this->root, $name, $value);
+        $param = new Parameter($this->root, $offset, $value);
         $this->parameters[$param->name] = $param;
     }
 
     /**
      * Removes one or more parameters with the specified name.
      *
-     * @param string $name
+     * @param string|int $offset
      */
     #[\ReturnTypeWillChange]
-    public function offsetUnset($name)
+    public function offsetUnset($offset): void
     {
-        if (is_int($name)) {
-            parent::offsetUnset($name);
+        if (is_int($offset)) {
+            parent::offsetUnset($offset);
+
             // @codeCoverageIgnoreStart
             // This will never be reached, because an exception is always
             // thrown.
@@ -469,7 +439,7 @@ public function offsetUnset($name)
             // @codeCoverageIgnoreEnd
         }
 
-        unset($this->parameters[strtoupper($name)]);
+        unset($this->parameters[strtoupper($offset)]);
     }
 
     /* }}} */
@@ -499,12 +469,8 @@ public function __clone()
      *    * level - (number between 1 and 3 with severity information)
      *    * message - (human readable message)
      *    * node - (reference to the offending node)
-     *
-     * @param int $options
-     *
-     * @return array
      */
-    public function validate($options = 0)
+    public function validate(int $options = 0): array
     {
         $warnings = [];
 
@@ -514,10 +480,8 @@ public function validate($options = 0)
             $level = 3;
             if ($options & self::REPAIR) {
                 $newValue = StringUtil::convertToUTF8($oldValue);
-                if (true || StringUtil::isUTF8($newValue)) {
-                    $this->setRawMimeDirValue($newValue);
-                    $level = 1;
-                }
+                $this->setRawMimeDirValue($newValue);
+                $level = 1;
             }
 
             if (preg_match('%([\x00-\x08\x0B-\x0C\x0E-\x1F\x7F])%', $oldValue, $matches)) {
@@ -533,11 +497,11 @@ public function validate($options = 0)
             ];
         }
 
-        // Checking if the propertyname does not contain any invalid bytes.
+        // Checking if the property name does not contain any invalid bytes.
         if (!preg_match('/^([A-Z0-9-]+)$/', $this->name)) {
             $warnings[] = [
                 'level' => $options & self::REPAIR ? 1 : 3,
-                'message' => 'The propertyname: '.$this->name.' contains invalid characters. Only A-Z, 0-9 and - are allowed',
+                'message' => 'The property name: '.$this->name.' contains invalid characters. Only A-Z, 0-9 and - are allowed',
                 'node' => $this,
             ];
             if ($options & self::REPAIR) {
@@ -546,7 +510,7 @@ public function validate($options = 0)
                     str_replace('_', '-', $this->name)
                 );
                 // Removing every other invalid character
-                $this->name = preg_replace('/([^A-Z0-9-])/u', '', $this->name);
+                $this->name = \preg_replace('/([^A-Z0-9-])/u', '', $this->name);
             }
         }
 
@@ -558,6 +522,7 @@ public function validate($options = 0)
                     'node' => $this,
                 ];
             } else {
+                /** @var Property $encoding */
                 $encoding = (string) $encoding;
 
                 $allowedEncoding = [];
@@ -571,7 +536,7 @@ public function validate($options = 0)
                         break;
                     case Document::VCARD30:
                         $allowedEncoding = ['B'];
-                        //Repair vCard30 that use BASE64 encoding
+                        // Repair vCard30 that use BASE64 encoding
                         if ($options & self::REPAIR) {
                             if ('BASE64' === strtoupper($encoding)) {
                                 $encoding = 'B';
@@ -609,7 +574,7 @@ public function validate($options = 0)
      * It's intended to remove all circular references, so PHP can easily clean
      * it up.
      */
-    public function destroy()
+    public function destroy(): void
     {
         parent::destroy();
         foreach ($this->parameters as $param) {
diff --git a/lib/Property/Binary.php b/lib/Property/Binary.php
index 1262dd054..25cda8d25 100644
--- a/lib/Property/Binary.php
+++ b/lib/Property/Binary.php
@@ -23,10 +23,8 @@ class Binary extends Property
     /**
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
-     *
-     * @var string
      */
-    public $delimiter = '';
+    public string $delimiter = '';
 
     /**
      * Updates the current value.
@@ -35,7 +33,7 @@ class Binary extends Property
      *
      * @param string|array $value
      */
-    public function setValue($value)
+    public function setValue($value): void
     {
         if (is_array($value)) {
             if (1 === count($value)) {
@@ -53,20 +51,16 @@ public function setValue($value)
      *
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
-     *
-     * @param string $val
      */
-    public function setRawMimeDirValue($val)
+    public function setRawMimeDirValue(string $val): void
     {
         $this->value = base64_decode($val);
     }
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    public function getRawMimeDirValue()
+    public function getRawMimeDirValue(): string
     {
         return base64_encode($this->value);
     }
@@ -76,10 +70,8 @@ public function getRawMimeDirValue()
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'BINARY';
     }
@@ -88,10 +80,8 @@ public function getValueType()
      * Returns the value, in the format it should be encoded for json.
      *
      * This method must always return an array.
-     *
-     * @return array
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         return [base64_encode($this->getValue())];
     }
@@ -101,7 +91,7 @@ public function getJsonValue()
      *
      * The value must always be an array.
      */
-    public function setJsonValue(array $value)
+    public function setJsonValue(array $value): void
     {
         $value = array_map('base64_decode', $value);
         parent::setJsonValue($value);
diff --git a/lib/Property/Boolean.php b/lib/Property/Boolean.php
index 4bd6ffdfe..cdc3408aa 100644
--- a/lib/Property/Boolean.php
+++ b/lib/Property/Boolean.php
@@ -23,21 +23,17 @@ class Boolean extends Property
      *
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
-     *
-     * @param string $val
      */
-    public function setRawMimeDirValue($val)
+    public function setRawMimeDirValue(string $val): void
     {
-        $val = 'TRUE' === strtoupper($val) ? true : false;
+        $val = 'TRUE' === strtoupper($val);
         $this->setValue($val);
     }
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    public function getRawMimeDirValue()
+    public function getRawMimeDirValue(): string
     {
         return $this->value ? 'TRUE' : 'FALSE';
     }
@@ -47,19 +43,17 @@ public function getRawMimeDirValue()
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'BOOLEAN';
     }
 
     /**
-     * Hydrate data from a XML subtree, as it would appear in a xCard or xCal
+     * Hydrate data from an XML subtree, as it would appear in a xCard or xCal
      * object.
      */
-    public function setXmlValue(array $value)
+    public function setXmlValue(array $value): void
     {
         $value = array_map(
             function ($value) {
diff --git a/lib/Property/FlatText.php b/lib/Property/FlatText.php
index d15cfe051..eee1316e2 100644
--- a/lib/Property/FlatText.php
+++ b/lib/Property/FlatText.php
@@ -2,20 +2,22 @@
 
 namespace Sabre\VObject\Property;
 
+use Sabre\VObject\InvalidDataException;
+
 /**
  * FlatText property.
  *
  * This object represents certain TEXT values.
  *
  * Specifically, this property is used for text values where there is only 1
- * part. Semi-colons and colons will be de-escaped when deserializing, but if
- * any semi-colons or commas appear without a backslash, we will not assume
+ * part. Semicolons and colons will be de-escaped when deserializing, but if
+ * any semicolons or commas appear without a backslash, we will not assume
  * that they are delimiters.
  *
- * vCard 2.1 specifically has a whole bunch of properties where this may
+ * vCard 2.1 specifically has a bunch of properties where this may
  * happen, as it only defines a delimiter for a few properties.
  *
- * vCard 4.0 states something similar. An unescaped semi-colon _may_ be a
+ * vCard 4.0 states something similar. An unescaped semicolon _may_ be a
  * delimiter, depending on the property.
  *
  * @copyright Copyright (C) fruux GmbH (https://fruux.com/)
@@ -26,19 +28,17 @@ class FlatText extends Text
 {
     /**
      * Field separator.
-     *
-     * @var string
      */
-    public $delimiter = ',';
+    public string $delimiter = ',';
 
     /**
      * Sets the value as a quoted-printable encoded string.
      *
-     * Overriding this so we're not splitting on a ; delimiter.
+     * Overriding this so that we're not splitting on a semicolon delimiter.
      *
-     * @param string $val
+     * @throws InvalidDataException
      */
-    public function setQuotedPrintableValue($val)
+    public function setQuotedPrintableValue(string $val): void
     {
         $val = quoted_printable_decode($val);
         $this->setValue($val);
diff --git a/lib/Property/FloatValue.php b/lib/Property/FloatValue.php
index e780ae6c1..7a36e0976 100644
--- a/lib/Property/FloatValue.php
+++ b/lib/Property/FloatValue.php
@@ -20,20 +20,16 @@ class FloatValue extends Property
     /**
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
-     *
-     * @var string
      */
-    public $delimiter = ';';
+    public string $delimiter = ';';
 
     /**
      * Sets a raw value coming from a mimedir (iCalendar/vCard) file.
      *
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
-     *
-     * @param string $val
      */
-    public function setRawMimeDirValue($val)
+    public function setRawMimeDirValue(string $val): void
     {
         $val = explode($this->delimiter, $val);
         foreach ($val as &$item) {
@@ -44,10 +40,8 @@ public function setRawMimeDirValue($val)
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    public function getRawMimeDirValue()
+    public function getRawMimeDirValue(): string
     {
         return implode(
             $this->delimiter,
@@ -60,10 +54,8 @@ public function getRawMimeDirValue()
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'FLOAT';
     }
@@ -72,10 +64,8 @@ public function getValueType()
      * Returns the value, in the format it should be encoded for JSON.
      *
      * This method must always return an array.
-     *
-     * @return array
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         $val = array_map('floatval', $this->getParts());
 
@@ -91,10 +81,10 @@ public function getJsonValue()
     }
 
     /**
-     * Hydrate data from a XML subtree, as it would appear in a xCard or xCal
+     * Hydrate data from an XML subtree, as it would appear in a xCard or xCal
      * object.
      */
-    public function setXmlValue(array $value)
+    public function setXmlValue(array $value): void
     {
         $value = array_map('floatval', $value);
         parent::setXmlValue($value);
@@ -103,10 +93,8 @@ public function setXmlValue(array $value)
     /**
      * This method serializes only the value of a property. This is used to
      * create xCard or xCal documents.
-     *
-     * @param Xml\Writer $writer XML writer
      */
-    protected function xmlSerializeValue(Xml\Writer $writer)
+    protected function xmlSerializeValue(Xml\Writer $writer): void
     {
         // Special-casing the GEO property.
         //
diff --git a/lib/Property/ICalendar/CalAddress.php b/lib/Property/ICalendar/CalAddress.php
index 2dbbc6eaf..01969e87d 100644
--- a/lib/Property/ICalendar/CalAddress.php
+++ b/lib/Property/ICalendar/CalAddress.php
@@ -18,20 +18,16 @@ class CalAddress extends Text
     /**
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
-     *
-     * @var string
      */
-    public $delimiter = '';
+    public string $delimiter = '';
 
     /**
      * Returns the type of value.
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'CAL-ADDRESS';
     }
@@ -43,17 +39,19 @@ public function getValueType()
      * uris to lower-case.
      *
      * Evolution in particular tends to encode mailto: as MAILTO:.
-     *
-     * @return string
      */
-    public function getNormalizedValue()
+    public function getNormalizedValue(): string
     {
         $input = $this->getValue();
         if (!strpos($input, ':')) {
             return $input;
         }
         list($schema, $everythingElse) = explode(':', $input, 2);
+        $schema = strtolower($schema);
+        if ('mailto' === $schema) {
+            $everythingElse = strtolower($everythingElse);
+        }
 
-        return strtolower($schema).':'.$everythingElse;
+        return $schema.':'.$everythingElse;
     }
 }
diff --git a/lib/Property/ICalendar/DateTime.php b/lib/Property/ICalendar/DateTime.php
index afeb8ff81..1892991a2 100644
--- a/lib/Property/ICalendar/DateTime.php
+++ b/lib/Property/ICalendar/DateTime.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\Property\ICalendar;
 
-use DateTimeInterface;
-use DateTimeZone;
 use Sabre\VObject\DateTimeParser;
 use Sabre\VObject\InvalidDataException;
 use Sabre\VObject\Property;
@@ -32,16 +30,18 @@ class DateTime extends Property
      *
      * @var string|null
      */
-    public $delimiter = ',';
+    public string $delimiter = ',';
 
     /**
      * Sets a multi-valued property.
      *
      * You may also specify DateTime objects here.
+     *
+     * @throws InvalidDataException
      */
-    public function setParts(array $parts)
+    public function setParts(array $parts): void
     {
-        if (isset($parts[0]) && $parts[0] instanceof DateTimeInterface) {
+        if (isset($parts[0]) && $parts[0] instanceof \DateTimeInterface) {
             $this->setDateTimes($parts);
         } else {
             parent::setParts($parts);
@@ -55,13 +55,15 @@ public function setParts(array $parts)
      *
      * Instead of strings, you may also use DateTime here.
      *
-     * @param string|array|DateTimeInterface $value
+     * @param string|array|\DateTimeInterface $value
+     *
+     * @throws InvalidDataException
      */
-    public function setValue($value)
+    public function setValue($value): void
     {
-        if (is_array($value) && isset($value[0]) && $value[0] instanceof DateTimeInterface) {
+        if (is_array($value) && isset($value[0]) && $value[0] instanceof \DateTimeInterface) {
             $this->setDateTimes($value);
-        } elseif ($value instanceof DateTimeInterface) {
+        } elseif ($value instanceof \DateTimeInterface) {
             $this->setDateTimes([$value]);
         } else {
             parent::setValue($value);
@@ -74,29 +76,25 @@ public function setValue($value)
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
      *
-     * @param string $val
+     * @throws InvalidDataException
      */
-    public function setRawMimeDirValue($val)
+    public function setRawMimeDirValue(string $val): void
     {
         $this->setValue(explode($this->delimiter, $val));
     }
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    public function getRawMimeDirValue()
+    public function getRawMimeDirValue(): string
     {
         return implode($this->delimiter, $this->getParts());
     }
 
     /**
      * Returns true if this is a DATE-TIME value, false if it's a DATE.
-     *
-     * @return bool
      */
-    public function hasTime()
+    public function hasTime(): bool
     {
         return 'DATE' !== strtoupper((string) $this['VALUE']);
     }
@@ -106,13 +104,13 @@ public function hasTime()
      *
      * Note that DATE is always floating.
      */
-    public function isFloating()
+    public function isFloating(): bool
     {
         return
-            !$this->hasTime() ||
-            (
-                !isset($this['TZID']) &&
-                false === strpos($this->getValue(), 'Z')
+            !$this->hasTime()
+            || (
+                !isset($this['TZID'])
+                && false === strpos($this->getValue(), 'Z')
             );
     }
 
@@ -127,15 +125,13 @@ public function isFloating()
      * property or floating time, we will use the DateTimeZone argument to
      * figure out the exact date.
      *
-     * @param DateTimeZone $timeZone
-     *
-     * @return \DateTimeImmutable
+     * @throws InvalidDataException
      */
-    public function getDateTime(DateTimeZone $timeZone = null, bool $activeCustomizedGuesser = true)
+    public function getDateTime(\DateTimeZone $timeZone = null, bool $activeCustomizedGuesser = true): ?\DateTimeImmutable
     {
         $dt = $this->getDateTimes($timeZone, $activeCustomizedGuesser);
         if (!$dt) {
-            return;
+            return null;
         }
 
         return $dt[0];
@@ -148,14 +144,14 @@ public function getDateTime(DateTimeZone $timeZone = null, bool $activeCustomize
      * property or floating time, we will use the DateTimeZone argument to
      * figure out the exact date.
      *
-     * @param DateTimeZone $timeZone
+     * @return \DateInterval[]|\DateTimeImmutable[]
      *
-     * @return \DateTimeImmutable[]
-     * @return \DateTime[]
+     * @throws InvalidDataException
      */
-    public function getDateTimes(DateTimeZone $timeZone = null, bool $activeCustomizedGuesser = true)
+    public function getDateTimes(\DateTimeZone $timeZone = null, bool $activeCustomizedGuesser = true): array
     {
         // Does the property have a TZID?
+        /** @var Property\FlatText $tzid */
         $tzid = $this['TZID'];
 
         if ($tzid) {
@@ -174,8 +170,10 @@ public function getDateTimes(DateTimeZone $timeZone = null, bool $activeCustomiz
      * Sets the property as a DateTime object.
      *
      * @param bool isFloating If set to true, timezones will be ignored
+     *
+     * @throws InvalidDataException
      */
-    public function setDateTime(DateTimeInterface $dt, $isFloating = false)
+    public function setDateTime(\DateTimeInterface $dt, $isFloating = false): void
     {
         $this->setDateTimes([$dt], $isFloating);
     }
@@ -186,10 +184,12 @@ public function setDateTime(DateTimeInterface $dt, $isFloating = false)
      * The first value will be used as a reference for the timezones, and all
      * the other values will be adjusted for that timezone
      *
-     * @param DateTimeInterface[] $dt
+     * @param \DateTimeInterface[] $dt
      * @param bool isFloating If set to true, timezones will be ignored
+     *
+     * @throws InvalidDataException
      */
-    public function setDateTimes(array $dt, $isFloating = false)
+    public function setDateTimes(array $dt, $isFloating = false): void
     {
         $values = [];
 
@@ -236,10 +236,8 @@ public function setDateTimes(array $dt, $isFloating = false)
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return $this->hasTime() ? 'DATE-TIME' : 'DATE';
     }
@@ -249,19 +247,19 @@ public function getValueType()
      *
      * This method must always return an array.
      *
-     * @return array
+     * @throws InvalidDataException
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         $dts = $this->getDateTimes();
         $hasTime = $this->hasTime();
         $isFloating = $this->isFloating();
 
         $tz = $dts[0]->getTimeZone();
-        $isUtc = $isFloating ? false : in_array($tz->getName(), ['UTC', 'GMT', 'Z']);
+        $isUtc = !$isFloating && in_array($tz->getName(), ['UTC', 'GMT', 'Z']);
 
         return array_map(
-            function (DateTimeInterface $dt) use ($hasTime, $isUtc) {
+            function (\DateTimeInterface $dt) use ($hasTime, $isUtc) {
                 if ($hasTime) {
                     return $dt->format('Y-m-d\\TH:i:s').($isUtc ? 'Z' : '');
                 } else {
@@ -276,8 +274,10 @@ function (DateTimeInterface $dt) use ($hasTime, $isUtc) {
      * Sets the json value, as it would appear in a jCard or jCal object.
      *
      * The value must always be an array.
+     *
+     * @throws InvalidDataException
      */
-    public function setJsonValue(array $value)
+    public function setJsonValue(array $value): void
     {
         // dates and times in jCal have one difference to dates and times in
         // iCalendar. In jCal date-parts are separated by dashes, and
@@ -297,14 +297,15 @@ function ($item) {
      * We need to intercept offsetSet, because it may be used to alter the
      * VALUE from DATE-TIME to DATE or vice-versa.
      *
-     * @param string $name
-     * @param mixed  $value
+     * @param string|int $offset
+     *
+     * @throws InvalidDataException
      */
     #[\ReturnTypeWillChange]
-    public function offsetSet($name, $value)
+    public function offsetSet($offset, $value): void
     {
-        parent::offsetSet($name, $value);
-        if ('VALUE' !== strtoupper($name)) {
+        parent::offsetSet($offset, $value);
+        if ('VALUE' !== strtoupper($offset)) {
             return;
         }
 
@@ -329,12 +330,8 @@ public function offsetSet($name, $value)
      *   1 - The issue was repaired (only happens if REPAIR was turned on)
      *   2 - An inconsequential issue
      *   3 - A severe issue.
-     *
-     * @param int $options
-     *
-     * @return array
      */
-    public function validate($options = 0)
+    public function validate(int $options = 0): array
     {
         $messages = parent::validate($options);
         $valueType = $this->getValueType();
diff --git a/lib/Property/ICalendar/Duration.php b/lib/Property/ICalendar/Duration.php
index e18fe191e..e95f355f2 100644
--- a/lib/Property/ICalendar/Duration.php
+++ b/lib/Property/ICalendar/Duration.php
@@ -2,7 +2,9 @@
 
 namespace Sabre\VObject\Property\ICalendar;
 
+use DateInterval;
 use Sabre\VObject\DateTimeParser;
+use Sabre\VObject\InvalidDataException;
 use Sabre\VObject\Property;
 
 /**
@@ -21,30 +23,24 @@ class Duration extends Property
     /**
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
-     *
-     * @var string
      */
-    public $delimiter = ',';
+    public string $delimiter = ',';
 
     /**
      * Sets a raw value coming from a mimedir (iCalendar/vCard) file.
      *
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
-     *
-     * @param string $val
      */
-    public function setRawMimeDirValue($val)
+    public function setRawMimeDirValue(string $val): void
     {
         $this->setValue(explode($this->delimiter, $val));
     }
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    public function getRawMimeDirValue()
+    public function getRawMimeDirValue(): string
     {
         return implode($this->delimiter, $this->getParts());
     }
@@ -54,10 +50,8 @@ public function getRawMimeDirValue()
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'DURATION';
     }
@@ -67,9 +61,9 @@ public function getValueType()
      *
      * If the property has more than one value, only the first is returned.
      *
-     * @return \DateInterval
+     * @throws InvalidDataException
      */
-    public function getDateInterval()
+    public function getDateInterval(): \DateInterval
     {
         $parts = $this->getParts();
         $value = $parts[0];
diff --git a/lib/Property/ICalendar/Period.php b/lib/Property/ICalendar/Period.php
index ae8a78911..7632cb4d1 100644
--- a/lib/Property/ICalendar/Period.php
+++ b/lib/Property/ICalendar/Period.php
@@ -3,6 +3,7 @@
 namespace Sabre\VObject\Property\ICalendar;
 
 use Sabre\VObject\DateTimeParser;
+use Sabre\VObject\InvalidDataException;
 use Sabre\VObject\Property;
 use Sabre\Xml;
 
@@ -22,30 +23,24 @@ class Period extends Property
     /**
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
-     *
-     * @var string
      */
-    public $delimiter = ',';
+    public string $delimiter = ',';
 
     /**
      * Sets a raw value coming from a mimedir (iCalendar/vCard) file.
      *
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
-     *
-     * @param string $val
      */
-    public function setRawMimeDirValue($val)
+    public function setRawMimeDirValue(string $val): void
     {
         $this->setValue(explode($this->delimiter, $val));
     }
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    public function getRawMimeDirValue()
+    public function getRawMimeDirValue(): string
     {
         return implode($this->delimiter, $this->getParts());
     }
@@ -55,10 +50,8 @@ public function getRawMimeDirValue()
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'PERIOD';
     }
@@ -68,7 +61,7 @@ public function getValueType()
      *
      * The value must always be an array.
      */
-    public function setJsonValue(array $value)
+    public function setJsonValue(array $value): void
     {
         $value = array_map(
             function ($item) {
@@ -84,9 +77,9 @@ function ($item) {
      *
      * This method must always return an array.
      *
-     * @return array
+     * @throws InvalidDataException
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         $return = [];
         foreach ($this->getParts() as $item) {
@@ -116,9 +109,9 @@ public function getJsonValue()
      * This method serializes only the value of a property. This is used to
      * create xCard or xCal documents.
      *
-     * @param Xml\Writer $writer XML writer
+     * @throws InvalidDataException
      */
-    protected function xmlSerializeValue(Xml\Writer $writer)
+    protected function xmlSerializeValue(Xml\Writer $writer): void
     {
         $writer->startElement(strtolower($this->getValueType()));
         $value = $this->getJsonValue();
diff --git a/lib/Property/ICalendar/Recur.php b/lib/Property/ICalendar/Recur.php
index 3d632fec1..9a1e9e643 100644
--- a/lib/Property/ICalendar/Recur.php
+++ b/lib/Property/ICalendar/Recur.php
@@ -2,6 +2,8 @@
 
 namespace Sabre\VObject\Property\ICalendar;
 
+use Sabre\VObject\InvalidDataException;
+use Sabre\VObject\Node;
 use Sabre\VObject\Property;
 use Sabre\Xml;
 
@@ -24,6 +26,11 @@
  */
 class Recur extends Property
 {
+    /**
+     * Reference to the parent object, if this is not the top object.
+     */
+    public ?Node $parent;
+
     /**
      * Updates the current value.
      *
@@ -31,10 +38,10 @@ class Recur extends Property
      *
      * @param string|array $value
      */
-    public function setValue($value)
+    public function setValue($value): void
     {
         // If we're getting the data from json, we'll be receiving an object
-        if ($value instanceof \StdClass) {
+        if ($value instanceof \stdClass) {
             $value = (array) $value;
         }
 
@@ -73,10 +80,8 @@ public function setValue($value)
      * it as a string.
      *
      * To get the correct multi-value version, use getParts.
-     *
-     * @return string
      */
-    public function getValue()
+    public function getValue(): string
     {
         $out = [];
         foreach ($this->value as $key => $value) {
@@ -89,7 +94,7 @@ public function getValue()
     /**
      * Sets a multi-valued property.
      */
-    public function setParts(array $parts)
+    public function setParts(array $parts): void
     {
         $this->setValue($parts);
     }
@@ -99,10 +104,8 @@ public function setParts(array $parts)
      *
      * This method always returns an array, if there was only a single value,
      * it will still be wrapped in an array.
-     *
-     * @return array
      */
-    public function getParts()
+    public function getParts(): array
     {
         return $this->value;
     }
@@ -112,20 +115,16 @@ public function getParts()
      *
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
-     *
-     * @param string $val
      */
-    public function setRawMimeDirValue($val)
+    public function setRawMimeDirValue(string $val): void
     {
         $this->setValue($val);
     }
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    public function getRawMimeDirValue()
+    public function getRawMimeDirValue(): string
     {
         return $this->getValue();
     }
@@ -135,10 +134,8 @@ public function getRawMimeDirValue()
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'RECUR';
     }
@@ -148,9 +145,9 @@ public function getValueType()
      *
      * This method must always return an array.
      *
-     * @return array
+     * @throws InvalidDataException
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         $values = [];
         foreach ($this->getParts() as $k => $v) {
@@ -170,10 +167,8 @@ public function getJsonValue()
     /**
      * This method serializes only the value of a property. This is used to
      * create xCard or xCal documents.
-     *
-     * @param Xml\Writer $writer XML writer
      */
-    protected function xmlSerializeValue(Xml\Writer $writer)
+    protected function xmlSerializeValue(Xml\Writer $writer): void
     {
         $valueType = strtolower($this->getValueType());
 
@@ -184,12 +179,8 @@ protected function xmlSerializeValue(Xml\Writer $writer)
 
     /**
      * Parses an RRULE value string, and turns it into a struct-ish array.
-     *
-     * @param string $value
-     *
-     * @return array
      */
-    public static function stringToArray($value)
+    public static function stringToArray(string $value): array
     {
         $value = strtoupper($value);
         $newValue = [];
@@ -227,12 +218,8 @@ public static function stringToArray($value)
      *   1 - The issue was repaired (only happens if REPAIR was turned on)
      *   2 - An inconsequential issue
      *   3 - A severe issue.
-     *
-     * @param int $options
-     *
-     * @return array
      */
-    public function validate($options = 0)
+    public function validate(int $options = 0): array
     {
         $repair = ($options & self::REPAIR);
 
diff --git a/lib/Property/IntegerValue.php b/lib/Property/IntegerValue.php
index 3ae775214..f1ae55d17 100644
--- a/lib/Property/IntegerValue.php
+++ b/lib/Property/IntegerValue.php
@@ -21,20 +21,16 @@ class IntegerValue extends Property
      *
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
-     *
-     * @param string $val
      */
-    public function setRawMimeDirValue($val)
+    public function setRawMimeDirValue(string $val): void
     {
         $this->setValue((int) $val);
     }
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    public function getRawMimeDirValue()
+    public function getRawMimeDirValue(): string
     {
         return $this->value;
     }
@@ -44,10 +40,8 @@ public function getRawMimeDirValue()
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'INTEGER';
     }
@@ -56,19 +50,17 @@ public function getValueType()
      * Returns the value, in the format it should be encoded for json.
      *
      * This method must always return an array.
-     *
-     * @return array
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         return [(int) $this->getValue()];
     }
 
     /**
-     * Hydrate data from a XML subtree, as it would appear in a xCard or xCal
+     * Hydrate data from an XML subtree, as it would appear in a xCard or xCal
      * object.
      */
-    public function setXmlValue(array $value)
+    public function setXmlValue(array $value): void
     {
         $value = array_map('intval', $value);
         parent::setXmlValue($value);
diff --git a/lib/Property/Text.php b/lib/Property/Text.php
index ac8aa066b..c606ad812 100644
--- a/lib/Property/Text.php
+++ b/lib/Property/Text.php
@@ -4,6 +4,7 @@
 
 use Sabre\VObject\Component;
 use Sabre\VObject\Document;
+use Sabre\VObject\InvalidDataException;
 use Sabre\VObject\Parser\MimeDir;
 use Sabre\VObject\Property;
 use Sabre\Xml;
@@ -22,17 +23,13 @@ class Text extends Property
     /**
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
-     *
-     * @var string
      */
-    public $delimiter = ',';
+    public string $delimiter = ',';
 
     /**
      * List of properties that are considered 'structured'.
-     *
-     * @var array
      */
-    protected $structuredValues = [
+    protected array $structuredValues = [
         // vCard
         'N',
         'ADR',
@@ -49,10 +46,8 @@ class Text extends Property
      *
      * N must for instance be represented as 5 components, separated by ;, even
      * if the last few components are unused.
-     *
-     * @var array
      */
-    protected $minimumPropertyValues = [
+    protected array $minimumPropertyValues = [
         'N' => 5,
         'ADR' => 7,
     ];
@@ -65,18 +60,17 @@ class Text extends Property
      * Parameter objects.
      *
      * @param Component         $root       The root document
-     * @param string            $name
      * @param string|array|null $value
      * @param array             $parameters List of parameters
-     * @param string            $group      The vcard property group
+     * @param string|null       $group      The vcard property group
      */
-    public function __construct(Component $root, $name, $value = null, array $parameters = [], $group = null)
+    public function __construct(Component $root, string $name, $value = null, array $parameters = [], string $group = null)
     {
         // There's two types of multi-valued text properties:
         // 1. multivalue properties.
         // 2. structured value properties
         //
-        // The former is always separated by a comma, the latter by semi-colon.
+        // The former is always separated by a comma, the latter by semicolon.
         if (in_array($name, $this->structuredValues)) {
             $this->delimiter = ';';
         }
@@ -90,19 +84,17 @@ public function __construct(Component $root, $name, $value = null, array $parame
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
      *
-     * @param string $val
+     * @throws InvalidDataException
      */
-    public function setRawMimeDirValue($val)
+    public function setRawMimeDirValue(string $val): void
     {
         $this->setValue(MimeDir::unescapeValue($val, $this->delimiter));
     }
 
     /**
      * Sets the value as a quoted-printable encoded string.
-     *
-     * @param string $val
      */
-    public function setQuotedPrintableValue($val)
+    public function setQuotedPrintableValue(string $val): void
     {
         $val = quoted_printable_decode($val);
 
@@ -119,15 +111,13 @@ public function setQuotedPrintableValue($val)
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    public function getRawMimeDirValue()
+    public function getRawMimeDirValue(): string
     {
         $val = $this->getParts();
 
         if (isset($this->minimumPropertyValues[$this->name])) {
-            $val = array_pad($val, $this->minimumPropertyValues[$this->name], '');
+            $val = \array_pad($val, $this->minimumPropertyValues[$this->name], '');
         }
 
         foreach ($val as &$item) {
@@ -136,31 +126,31 @@ public function getRawMimeDirValue()
             }
 
             foreach ($item as &$subItem) {
-                $subItem = strtr(
-                    $subItem,
-                    [
-                        '\\' => '\\\\',
-                        ';' => '\;',
-                        ',' => '\,',
-                        "\n" => '\n',
-                        "\r" => '',
-                    ]
-                );
+                if (!\is_null($subItem)) {
+                    $subItem = strtr(
+                        $subItem,
+                        [
+                            '\\' => '\\\\',
+                            ';' => '\;',
+                            ',' => '\,',
+                            "\n" => '\n',
+                            "\r" => '',
+                        ]
+                    );
+                }
             }
-            $item = implode(',', $item);
+            $item = \implode(',', $item);
         }
 
-        return implode($this->delimiter, $val);
+        return \implode($this->delimiter, $val);
     }
 
     /**
      * Returns the value, in the format it should be encoded for json.
      *
      * This method must always return an array.
-     *
-     * @return array
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         // Structured text values should always be returned as a single
         // array-item. Multi-value text should be returned as multiple items in
@@ -177,20 +167,16 @@ public function getJsonValue()
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'TEXT';
     }
 
     /**
      * Turns the object back into a serialized blob.
-     *
-     * @return string
      */
-    public function serialize()
+    public function serialize(): string
     {
         // We need to kick in a special type of encoding, if it's a 2.1 vcard.
         if (Document::VCARD21 !== $this->root->getDocumentType()) {
@@ -230,7 +216,7 @@ public function serialize()
         if (false !== \strpos($val, "\n")) {
             $str .= ';ENCODING=QUOTED-PRINTABLE:';
             $lastLine = $str;
-            $out = null;
+            $out = '';
 
             // The PHP built-in quoted-printable-encode does not correctly
             // encode newlines for us. Specifically, the \r\n sequence must in
@@ -276,14 +262,12 @@ public function serialize()
     /**
      * This method serializes only the value of a property. This is used to
      * create xCard or xCal documents.
-     *
-     * @param Xml\Writer $writer XML writer
      */
-    protected function xmlSerializeValue(Xml\Writer $writer)
+    protected function xmlSerializeValue(Xml\Writer $writer): void
     {
         $values = $this->getParts();
 
-        $map = function ($items) use ($values, $writer) {
+        $map = function (array $items) use ($values, $writer): void {
             foreach ($items as $i => $item) {
                 $writer->writeElement(
                     $item,
@@ -360,26 +344,22 @@ protected function xmlSerializeValue(Xml\Writer $writer)
      *    * level - (number between 1 and 3 with severity information)
      *    * message - (human readable message)
      *    * node - (reference to the offending node)
-     *
-     * @param int $options
-     *
-     * @return array
      */
-    public function validate($options = 0)
+    public function validate(int $options = 0): array
     {
         $warnings = parent::validate($options);
 
         if (isset($this->minimumPropertyValues[$this->name])) {
             $minimum = $this->minimumPropertyValues[$this->name];
             $parts = $this->getParts();
-            if (count($parts) < $minimum) {
+            if (\count($parts) < $minimum) {
                 $warnings[] = [
                     'level' => $options & self::REPAIR ? 1 : 3,
-                    'message' => 'The '.$this->name.' property must have at least '.$minimum.' values. It only has '.count($parts),
+                    'message' => 'The '.$this->name.' property must have at least '.$minimum.' values. It only has '.\count($parts),
                     'node' => $this,
                 ];
                 if ($options & self::REPAIR) {
-                    $parts = array_pad($parts, $minimum, '');
+                    $parts = \array_pad($parts, $minimum, '');
                     $this->setParts($parts);
                 }
             }
diff --git a/lib/Property/Time.php b/lib/Property/Time.php
index 1b81609aa..ed314fc0d 100644
--- a/lib/Property/Time.php
+++ b/lib/Property/Time.php
@@ -3,6 +3,7 @@
 namespace Sabre\VObject\Property;
 
 use Sabre\VObject\DateTimeParser;
+use Sabre\VObject\InvalidDataException;
 
 /**
  * Time property.
@@ -18,20 +19,16 @@ class Time extends Text
     /**
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
-     *
-     * @var string
      */
-    public $delimiter = '';
+    public string $delimiter = '';
 
     /**
      * Returns the type of value.
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'TIME';
     }
@@ -41,7 +38,7 @@ public function getValueType()
      *
      * The value must always be an array.
      */
-    public function setJsonValue(array $value)
+    public function setJsonValue(array $value): void
     {
         // Removing colons from value.
         $value = str_replace(
@@ -62,9 +59,9 @@ public function setJsonValue(array $value)
      *
      * This method must always return an array.
      *
-     * @return array
+     * @throws InvalidDataException
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         $parts = DateTimeParser::parseVCardTime($this->getValue());
         $timeStr = '';
@@ -115,10 +112,10 @@ public function getJsonValue()
     }
 
     /**
-     * Hydrate data from a XML subtree, as it would appear in a xCard or xCal
+     * Hydrate data from an XML subtree, as it would appear in a xCard or xCal
      * object.
      */
-    public function setXmlValue(array $value)
+    public function setXmlValue(array $value): void
     {
         $value = array_map(
             function ($value) {
diff --git a/lib/Property/Unknown.php b/lib/Property/Unknown.php
index 6f404c286..3bcf61351 100644
--- a/lib/Property/Unknown.php
+++ b/lib/Property/Unknown.php
@@ -18,10 +18,8 @@ class Unknown extends Text
      * Returns the value, in the format it should be encoded for json.
      *
      * This method must always return an array.
-     *
-     * @return array
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         return [$this->getRawMimeDirValue()];
     }
@@ -31,10 +29,8 @@ public function getJsonValue()
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'UNKNOWN';
     }
diff --git a/lib/Property/Uri.php b/lib/Property/Uri.php
index 1ad1fb199..228b7090f 100644
--- a/lib/Property/Uri.php
+++ b/lib/Property/Uri.php
@@ -3,7 +3,6 @@
 namespace Sabre\VObject\Property;
 
 use Sabre\VObject\Parameter;
-use Sabre\VObject\Property;
 
 /**
  * URI property.
@@ -19,30 +18,24 @@ class Uri extends Text
     /**
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
-     *
-     * @var string
      */
-    public $delimiter = '';
+    public string $delimiter = '';
 
     /**
      * Returns the type of value.
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'URI';
     }
 
     /**
      * Returns an iterable list of children.
-     *
-     * @return array
      */
-    public function parameters()
+    public function parameters(): array
     {
         $parameters = parent::parameters();
         if (!isset($parameters['VALUE']) && in_array($this->name, ['URL', 'PHOTO'])) {
@@ -65,13 +58,11 @@ public function parameters()
      *
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
-     *
-     * @param string $val
      */
-    public function setRawMimeDirValue($val)
+    public function setRawMimeDirValue(string $val): void
     {
         // Normally we don't need to do any type of unescaping for these
-        // properties, however.. we've noticed that Google Contacts
+        // properties, however, we've noticed that Google Contacts
         // specifically escapes the colon (:) with a backslash. While I have
         // no clue why they thought that was a good idea, I'm unescaping it
         // anyway.
@@ -100,10 +91,8 @@ public function setRawMimeDirValue($val)
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    public function getRawMimeDirValue()
+    public function getRawMimeDirValue(): string
     {
         if (is_array($this->value)) {
             $value = $this->value[0];
diff --git a/lib/Property/UtcOffset.php b/lib/Property/UtcOffset.php
index 04b88447f..09aab0151 100644
--- a/lib/Property/UtcOffset.php
+++ b/lib/Property/UtcOffset.php
@@ -2,6 +2,8 @@
 
 namespace Sabre\VObject\Property;
 
+use Sabre\VObject\InvalidDataException;
+
 /**
  * UtcOffset property.
  *
@@ -16,20 +18,16 @@ class UtcOffset extends Text
     /**
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
-     *
-     * @var string
      */
-    public $delimiter = '';
+    public string $delimiter = '';
 
     /**
      * Returns the type of value.
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'UTC-OFFSET';
     }
@@ -38,8 +36,10 @@ public function getValueType()
      * Sets the JSON value, as it would appear in a jCard or jCal object.
      *
      * The value must always be an array.
+     *
+     * @throws InvalidDataException
      */
-    public function setJsonValue(array $value)
+    public function setJsonValue(array $value): void
     {
         $value = array_map(
             function ($value) {
@@ -54,10 +54,8 @@ function ($value) {
      * Returns the value, in the format it should be encoded for JSON.
      *
      * This method must always return an array.
-     *
-     * @return array
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         return array_map(
             function ($value) {
diff --git a/lib/Property/VCard/Date.php b/lib/Property/VCard/Date.php
index fc679d572..1ad9fedc2 100644
--- a/lib/Property/VCard/Date.php
+++ b/lib/Property/VCard/Date.php
@@ -18,10 +18,8 @@ class Date extends DateAndOrTime
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'DATE';
     }
@@ -29,7 +27,7 @@ public function getValueType()
     /**
      * Sets the property as a DateTime object.
      */
-    public function setDateTime(\DateTimeInterface $dt)
+    public function setDateTime(\DateTimeInterface $dt): void
     {
         $this->value = $dt->format('Ymd');
     }
diff --git a/lib/Property/VCard/DateAndOrTime.php b/lib/Property/VCard/DateAndOrTime.php
index 7bf79c48c..e87bf1b3a 100644
--- a/lib/Property/VCard/DateAndOrTime.php
+++ b/lib/Property/VCard/DateAndOrTime.php
@@ -3,7 +3,6 @@
 namespace Sabre\VObject\Property\VCard;
 
 use DateTime;
-use DateTimeImmutable;
 use DateTimeInterface;
 use Sabre\VObject\DateTimeParser;
 use Sabre\VObject\InvalidDataException;
@@ -23,20 +22,16 @@ class DateAndOrTime extends Property
 {
     /**
      * Field separator.
-     *
-     * @var string
      */
-    public $delimiter = '';
+    public string $delimiter = '';
 
     /**
      * Returns the type of value.
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'DATE-AND-OR-TIME';
     }
@@ -46,12 +41,12 @@ public function getValueType()
      *
      * You may also specify DateTimeInterface objects here.
      */
-    public function setParts(array $parts)
+    public function setParts(array $parts): void
     {
         if (count($parts) > 1) {
             throw new \InvalidArgumentException('Only one value allowed');
         }
-        if (isset($parts[0]) && $parts[0] instanceof DateTimeInterface) {
+        if (isset($parts[0]) && $parts[0] instanceof \DateTimeInterface) {
             $this->setDateTime($parts[0]);
         } else {
             parent::setParts($parts);
@@ -65,11 +60,11 @@ public function setParts(array $parts)
      *
      * Instead of strings, you may also use DateTimeInterface here.
      *
-     * @param string|array|DateTimeInterface $value
+     * @param string|array|\DateTimeInterface $value
      */
-    public function setValue($value)
+    public function setValue($value): void
     {
-        if ($value instanceof DateTimeInterface) {
+        if ($value instanceof \DateTimeInterface) {
             $this->setDateTime($value);
         } else {
             parent::setValue($value);
@@ -79,7 +74,7 @@ public function setValue($value)
     /**
      * Sets the property as a DateTime object.
      */
-    public function setDateTime(DateTimeInterface $dt)
+    public function setDateTime(\DateTimeInterface $dt): void
     {
         $tz = $dt->getTimeZone();
         $isUtc = in_array($tz->getName(), ['UTC', 'GMT', 'Z']);
@@ -108,11 +103,11 @@ public function setDateTime(DateTimeInterface $dt)
      * current values for those. So at the time of writing, if the year was
      * omitted, we would have filled in 2014.
      *
-     * @return DateTimeImmutable
+     * @throws InvalidDataException
      */
-    public function getDateTime()
+    public function getDateTime(): \DateTimeImmutable
     {
-        $now = new DateTime();
+        $now = new \DateTime();
 
         $tzFormat = 0 === $now->getTimezone()->getOffset($now) ? '\\Z' : 'O';
         $nowParts = DateTimeParser::parseVCardDateTime($now->format('Ymd\\This'.$tzFormat));
@@ -128,7 +123,7 @@ public function getDateTime()
             }
         }
 
-        return new DateTimeImmutable("$dateParts[year]-$dateParts[month]-$dateParts[date] $dateParts[hour]:$dateParts[minute]:$dateParts[second] $dateParts[timezone]");
+        return new \DateTimeImmutable("$dateParts[year]-$dateParts[month]-$dateParts[date] $dateParts[hour]:$dateParts[minute]:$dateParts[second] $dateParts[timezone]");
     }
 
     /**
@@ -136,9 +131,9 @@ public function getDateTime()
      *
      * This method must always return an array.
      *
-     * @return array
+     * @throws InvalidDataException
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         $parts = DateTimeParser::parseVCardDateTime($this->getValue());
 
@@ -228,16 +223,16 @@ public function getJsonValue()
      * This method serializes only the value of a property. This is used to
      * create xCard or xCal documents.
      *
-     * @param Xml\Writer $writer XML writer
+     * @throws InvalidDataException
      */
-    protected function xmlSerializeValue(Xml\Writer $writer)
+    protected function xmlSerializeValue(Xml\Writer $writer): void
     {
         $valueType = strtolower($this->getValueType());
         $parts = DateTimeParser::parseVCardDateAndOrTime($this->getValue());
         $value = '';
 
         // $d = defined
-        $d = function ($part) use ($parts) {
+        $d = function ($part) use ($parts): bool {
             return !is_null($parts[$part]);
         };
 
@@ -264,7 +259,7 @@ protected function xmlSerializeValue(Xml\Writer $writer)
                 $value .= '---'.$r('date');
             }
 
-            // # 4.3.2
+        // # 4.3.2
         // value-time = element time {
         //     xsd:string { pattern = "(\d\d(\d\d(\d\d)?)?|-\d\d(\d\d?)|--\d\d)"
         //                          ~ "(Z|[+\-]\d\d(\d\d)?)?" }
@@ -307,20 +302,16 @@ protected function xmlSerializeValue(Xml\Writer $writer)
      *
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
-     *
-     * @param string $val
      */
-    public function setRawMimeDirValue($val)
+    public function setRawMimeDirValue(string $val): void
     {
         $this->setValue($val);
     }
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    public function getRawMimeDirValue()
+    public function getRawMimeDirValue(): string
     {
         return implode($this->delimiter, $this->getParts());
     }
@@ -342,12 +333,8 @@ public function getRawMimeDirValue()
      *   1 - The issue was repaired (only happens if REPAIR was turned on)
      *   2 - An inconsequential issue
      *   3 - A severe issue.
-     *
-     * @param int $options
-     *
-     * @return array
      */
-    public function validate($options = 0)
+    public function validate(int $options = 0): array
     {
         $messages = parent::validate($options);
         $value = $this->getValue();
diff --git a/lib/Property/VCard/DateTime.php b/lib/Property/VCard/DateTime.php
index 49c1f3555..c71071f1a 100644
--- a/lib/Property/VCard/DateTime.php
+++ b/lib/Property/VCard/DateTime.php
@@ -18,10 +18,8 @@ class DateTime extends DateAndOrTime
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'DATE-TIME';
     }
diff --git a/lib/Property/VCard/LanguageTag.php b/lib/Property/VCard/LanguageTag.php
index 318ea0231..c3b996f52 100644
--- a/lib/Property/VCard/LanguageTag.php
+++ b/lib/Property/VCard/LanguageTag.php
@@ -20,20 +20,16 @@ class LanguageTag extends Property
      *
      * This has been 'unfolded', so only 1 line will be passed. Unescaping is
      * not yet done, but parameters are not included.
-     *
-     * @param string $val
      */
-    public function setRawMimeDirValue($val)
+    public function setRawMimeDirValue(string $val): void
     {
         $this->setValue($val);
     }
 
     /**
      * Returns a raw mime-dir representation of the value.
-     *
-     * @return string
      */
-    public function getRawMimeDirValue()
+    public function getRawMimeDirValue(): string
     {
         return $this->getValue();
     }
@@ -43,10 +39,8 @@ public function getRawMimeDirValue()
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'LANGUAGE-TAG';
     }
diff --git a/lib/Property/VCard/PhoneNumber.php b/lib/Property/VCard/PhoneNumber.php
index b714ffd03..f007be3df 100644
--- a/lib/Property/VCard/PhoneNumber.php
+++ b/lib/Property/VCard/PhoneNumber.php
@@ -13,17 +13,15 @@
  */
 class PhoneNumber extends Property\Text
 {
-    protected $structuredValues = [];
+    protected array $structuredValues = [];
 
     /**
      * Returns the type of value.
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'PHONE-NUMBER';
     }
diff --git a/lib/Property/VCard/TimeStamp.php b/lib/Property/VCard/TimeStamp.php
index da6ea3d44..80739237e 100644
--- a/lib/Property/VCard/TimeStamp.php
+++ b/lib/Property/VCard/TimeStamp.php
@@ -3,6 +3,7 @@
 namespace Sabre\VObject\Property\VCard;
 
 use Sabre\VObject\DateTimeParser;
+use Sabre\VObject\InvalidDataException;
 use Sabre\VObject\Property\Text;
 use Sabre\Xml;
 
@@ -20,20 +21,16 @@ class TimeStamp extends Text
     /**
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
-     *
-     * @var string
      */
-    public $delimiter = '';
+    public string $delimiter = '';
 
     /**
      * Returns the type of value.
      *
      * This corresponds to the VALUE= parameter. Every property also has a
      * 'default' valueType.
-     *
-     * @return string
      */
-    public function getValueType()
+    public function getValueType(): string
     {
         return 'TIMESTAMP';
     }
@@ -43,9 +40,9 @@ public function getValueType()
      *
      * This method must always return an array.
      *
-     * @return array
+     * @throws InvalidDataException
      */
-    public function getJsonValue()
+    public function getJsonValue(): array
     {
         $parts = DateTimeParser::parseVCardDateTime($this->getValue());
 
@@ -68,10 +65,8 @@ public function getJsonValue()
     /**
      * This method serializes only the value of a property. This is used to
      * create xCard or xCal documents.
-     *
-     * @param Xml\Writer $writer XML writer
      */
-    protected function xmlSerializeValue(Xml\Writer $writer)
+    protected function xmlSerializeValue(Xml\Writer $writer): void
     {
         // xCard is the only XML and JSON format that has the same date and time
         // format than vCard.
diff --git a/lib/Reader.php b/lib/Reader.php
index a68c1af47..fc9c58054 100644
--- a/lib/Reader.php
+++ b/lib/Reader.php
@@ -2,6 +2,8 @@
 
 namespace Sabre\VObject;
 
+use Sabre\Xml\LibXMLException;
+
 /**
  * iCalendar/vCard/jCal/jCard/xCal/xCard reader object.
  *
@@ -18,18 +20,18 @@ class Reader
      * If this option is passed to the reader, it will be less strict about the
      * validity of the lines.
      */
-    const OPTION_FORGIVING = 1;
+    public const OPTION_FORGIVING = 1;
 
     /**
      * If this option is turned on, any lines we cannot parse will be ignored
      * by the reader.
      */
-    const OPTION_IGNORE_INVALID_LINES = 2;
+    public const OPTION_IGNORE_INVALID_LINES = 2;
 
     /**
      * If this option is turned on, it will fix unfolding parse error by adding empty space.
      */
-    const OPTION_FIX_UNFOLDING = 4;
+    public const OPTION_FIX_UNFOLDING = 4;
 
     /**
      * Parses a vCard or iCalendar object, and returns the top component.
@@ -40,18 +42,15 @@ class Reader
      * You can either supply a string, or a readable stream for input.
      *
      * @param string|resource $data
-     * @param int             $options
-     * @param string          $charset
      *
-     * @return Document
+     * @throws ParseException
      */
-    public static function read($data, $options = 0, $charset = 'UTF-8')
+    public static function read($data, int $options = 0, string $charset = 'UTF-8'): ?Document
     {
         $parser = new Parser\MimeDir();
         $parser->setCharset($charset);
-        $result = $parser->parse($data, $options);
 
-        return $result;
+        return $parser->parse($data, $options);
     }
 
     /**
@@ -65,16 +64,15 @@ public static function read($data, $options = 0, $charset = 'UTF-8')
      * input.
      *
      * @param string|resource|array $data
-     * @param int                   $options
      *
-     * @return Document
+     * @throws EofException
+     * @throws ParseException|InvalidDataException
      */
-    public static function readJson($data, $options = 0)
+    public static function readJson($data, int $options = 0): ?Document
     {
         $parser = new Parser\Json();
-        $result = $parser->parse($data, $options);
 
-        return $result;
+        return $parser->parse($data, $options);
     }
 
     /**
@@ -86,15 +84,16 @@ public static function readJson($data, $options = 0)
      * You can either supply a string, or a readable stream for input.
      *
      * @param string|resource $data
-     * @param int             $options
      *
-     * @return Document
+     * @throws EofException
+     * @throws InvalidDataException
+     * @throws ParseException
+     * @throws LibXMLException
      */
-    public static function readXML($data, $options = 0)
+    public static function readXML($data, int $options = 0): ?Document
     {
         $parser = new Parser\XML();
-        $result = $parser->parse($data, $options);
 
-        return $result;
+        return $parser->parse($data, $options);
     }
 }
diff --git a/lib/Recur/EventIterator.php b/lib/Recur/EventIterator.php
index 61f05d7de..d79cf3132 100644
--- a/lib/Recur/EventIterator.php
+++ b/lib/Recur/EventIterator.php
@@ -2,12 +2,9 @@
 
 namespace Sabre\VObject\Recur;
 
-use DateTimeImmutable;
-use DateTimeInterface;
-use DateTimeZone;
-use InvalidArgumentException;
 use Sabre\VObject\Component;
 use Sabre\VObject\Component\VEvent;
+use Sabre\VObject\InvalidDataException;
 use Sabre\VObject\Settings;
 
 /**
@@ -62,17 +59,13 @@ class EventIterator implements \Iterator
 {
     /**
      * Reference timeZone for floating dates and times.
-     *
-     * @var DateTimeZone
      */
-    protected $timeZone;
+    protected \DateTimeZone $timeZone;
 
     /**
      * True if we're iterating an all-day event.
-     *
-     * @var bool
      */
-    protected $allDay = false;
+    protected bool $allDay = false;
 
     /**
      * Creates the iterator.
@@ -88,15 +81,18 @@ class EventIterator implements \Iterator
      *
      * The $uid parameter is only required for the first method.
      *
-     * @param Component|array $input
-     * @param string|null     $uid
-     * @param DateTimeZone    $timeZone reference timezone for floating dates and
-     *                                  times
+     * @param Component|Component\VCalendar|array $input
+     * @param \DateTimeZone|null                  $timeZone reference timezone for floating dates and
+     *                                                      times
+     *
+     * @throws MaxInstancesExceededException
+     * @throws NoInstancesException
+     * @throws InvalidDataException
      */
-    public function __construct($input, $uid = null, DateTimeZone $timeZone = null)
+    public function __construct($input, string $uid = null, \DateTimeZone $timeZone = null)
     {
         if (is_null($timeZone)) {
-            $timeZone = new DateTimeZone('UTC');
+            $timeZone = new \DateTimeZone('UTC');
         }
         $this->timeZone = $timeZone;
 
@@ -107,16 +103,16 @@ public function __construct($input, $uid = null, DateTimeZone $timeZone = null)
             $events = [$input];
         } else {
             // Calendar + UID mode.
-            $uid = (string) $uid;
             if (!$uid) {
-                throw new InvalidArgumentException('The UID argument is required when a VCALENDAR is passed to this constructor');
+                throw new \InvalidArgumentException('The UID argument is required when a VCALENDAR is passed to this constructor');
             }
             if (!isset($input->VEVENT)) {
-                throw new InvalidArgumentException('No events found in this calendar');
+                throw new \InvalidArgumentException('No events found in this calendar');
             }
             $events = $input->getByUID($uid);
         }
 
+        /** @var VEvent[] $events */
         foreach ($events as $vevent) {
             if (!isset($vevent->{'RECURRENCE-ID'})) {
                 $this->masterEvent = $vevent;
@@ -136,7 +132,7 @@ public function __construct($input, $uid = null, DateTimeZone $timeZone = null)
             // event and use that instead. This may not always give the
             // desired result.
             if (!count($this->overriddenEvents)) {
-                throw new InvalidArgumentException('This VCALENDAR did not have an event with UID: '.$uid);
+                throw new \InvalidArgumentException('This VCALENDAR did not have an event with UID: '.$uid);
             }
             $this->masterEvent = array_shift($this->overriddenEvents);
         }
@@ -195,40 +191,40 @@ public function __construct($input, $uid = null, DateTimeZone $timeZone = null)
 
     /**
      * Returns the date for the current position of the iterator.
-     *
-     * @return DateTimeImmutable
      */
     #[\ReturnTypeWillChange]
-    public function current()
+    public function current(): ?\DateTimeImmutable
     {
         if ($this->currentDate) {
             return clone $this->currentDate;
         }
+
+        return null;
     }
 
     /**
      * This method returns the start date for the current iteration of the
      * event.
-     *
-     * @return DateTimeImmutable
      */
-    public function getDtStart()
+    public function getDtStart(): ?\DateTimeImmutable
     {
         if ($this->currentDate) {
             return clone $this->currentDate;
         }
+
+        return null;
     }
 
     /**
      * This method returns the end date for the current iteration of the
      * event.
      *
-     * @return DateTimeImmutable
+     * @throws MaxInstancesExceededException|InvalidDataException
      */
-    public function getDtEnd()
+    public function getDtEnd(): ?\DateTimeImmutable
     {
         if (!$this->valid()) {
-            return;
+            return null;
         }
         if ($this->currentOverriddenEvent && $this->currentOverriddenEvent->DTEND) {
             return $this->currentOverriddenEvent->DTEND->getDateTime($this->timeZone);
@@ -245,14 +241,16 @@ public function getDtEnd()
      * This VEVENT will have a recurrence id, and its DTSTART and DTEND
      * altered.
      *
-     * @return VEvent
+     * @throws MaxInstancesExceededException
+     * @throws InvalidDataException
      */
-    public function getEventObject()
+    public function getEventObject(): VEvent
     {
         if ($this->currentOverriddenEvent) {
             return $this->currentOverriddenEvent;
         }
 
+        /** @var VEvent $event */
         $event = clone $this->masterEvent;
 
         // Ignoring the following block, because PHPUnit's code coverage
@@ -283,11 +281,9 @@ public function getEventObject()
      * Returns the current position of the iterator.
      *
      * This is for us simply a 0-based index.
-     *
-     * @return int
      */
     #[\ReturnTypeWillChange]
-    public function key()
+    public function key(): int
     {
         // The counter is always 1 ahead.
         return $this->counter - 1;
@@ -297,10 +293,10 @@ public function key()
      * This is called after next, to see if the iterator is still at a valid
      * position, or if it's at the end.
      *
-     * @return bool
+     * @throws MaxInstancesExceededException
      */
     #[\ReturnTypeWillChange]
-    public function valid()
+    public function valid(): bool
     {
         if ($this->counter > Settings::$maxRecurrences && -1 !== Settings::$maxRecurrences) {
             throw new MaxInstancesExceededException('Recurring events are only allowed to generate '.Settings::$maxRecurrences);
@@ -312,15 +308,16 @@ public function valid()
     /**
      * Sets the iterator back to the starting point.
      *
-     * @return void
+     * @throws InvalidDataException
      */
     #[\ReturnTypeWillChange]
-    public function rewind()
+    public function rewind(): void
     {
         $this->recurIterator->rewind();
         // re-creating overridden event index.
         $index = [];
         foreach ($this->overriddenEvents as $key => $event) {
+            /** @var VEvent $event */
             $stamp = $event->DTSTART->getDateTime($this->timeZone)->getTimeStamp();
             $index[$stamp][] = $key;
         }
@@ -338,10 +335,10 @@ public function rewind()
     /**
      * Advances the iterator with one step.
      *
-     * @return void
+     * @throws InvalidDataException
      */
     #[\ReturnTypeWillChange]
-    public function next()
+    public function next(): void
     {
         $this->currentOverriddenEvent = null;
         ++$this->counter;
@@ -393,8 +390,10 @@ public function next()
 
     /**
      * Quickly jump to a date in the future.
+     *
+     * @throws MaxInstancesExceededException|InvalidDataException
      */
-    public function fastForward(DateTimeInterface $dateTime)
+    public function fastForward(\DateTimeInterface $dateTime): void
     {
         while ($this->valid() && $this->getDtEnd() <= $dateTime) {
             $this->next();
@@ -403,10 +402,8 @@ public function fastForward(DateTimeInterface $dateTime)
 
     /**
      * Returns true if this recurring event never ends.
-     *
-     * @return bool
      */
-    public function isInfinite()
+    public function isInfinite(): bool
     {
         return $this->recurIterator->isInfinite();
     }
@@ -414,9 +411,9 @@ public function isInfinite()
     /**
      * RRULE parser.
      *
-     * @var RRuleIterator
+     * @var RRuleIterator|RDateIterator
      */
-    protected $recurIterator;
+    protected \Iterator $recurIterator;
 
     /**
      * The duration, in seconds, of the master event.
@@ -427,71 +424,53 @@ public function isInfinite()
 
     /**
      * A reference to the main (master) event.
-     *
-     * @var VEVENT
      */
-    protected $masterEvent;
+    protected ?VEvent $masterEvent = null;
 
     /**
      * List of overridden events.
-     *
-     * @var array
      */
-    protected $overriddenEvents = [];
+    protected array $overriddenEvents = [];
 
     /**
      * Overridden event index.
      *
      * Key is timestamp, value is the list of indexes of the item in the $overriddenEvent
      * property.
-     *
-     * @var array
      */
-    protected $overriddenEventsIndex;
+    protected array $overriddenEventsIndex;
 
     /**
      * A list of recurrence-id's that are either part of EXDATE, or are
      * overridden.
-     *
-     * @var array
      */
-    protected $exceptions = [];
+    protected array $exceptions = [];
 
     /**
      * Internal event counter.
-     *
-     * @var int
      */
-    protected $counter;
+    protected int $counter = 0;
 
     /**
      * The very start of the iteration process.
-     *
-     * @var DateTimeImmutable
      */
-    protected $startDate;
+    protected ?\DateTimeImmutable $startDate;
 
     /**
      * Where we are currently in the iteration process.
-     *
-     * @var DateTimeImmutable
      */
-    protected $currentDate;
+    protected ?\DateTimeImmutable $currentDate = null;
 
     /**
      * The next date from the rrule parser.
      *
      * Sometimes we need to temporary store the next date, because an
      * overridden event came before.
-     *
-     * @var DateTimeImmutable
      */
-    protected $nextDate;
+    protected ?\DateTimeImmutable $nextDate = null;
 
     /**
      * The event that overwrites the current iteration.
-     *
-     * @var VEVENT
      */
-    protected $currentOverriddenEvent;
+    protected ?VEvent $currentOverriddenEvent = null;
 }
diff --git a/lib/Recur/MaxInstancesExceededException.php b/lib/Recur/MaxInstancesExceededException.php
index cb0835813..38d62b46b 100644
--- a/lib/Recur/MaxInstancesExceededException.php
+++ b/lib/Recur/MaxInstancesExceededException.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\Recur;
 
-use Exception;
-
 /**
  * This exception will get thrown when a recurrence rule generated more than
  * the maximum number of instances.
@@ -12,6 +10,6 @@
  * @author Evert Pot (http://evertpot.com/)
  * @license http://code.google.com/p/sabredav/wiki/License Modified BSD License
  */
-class MaxInstancesExceededException extends Exception
+class MaxInstancesExceededException extends \Exception
 {
 }
diff --git a/lib/Recur/NoInstancesException.php b/lib/Recur/NoInstancesException.php
index 348c02306..4c2d44aa6 100644
--- a/lib/Recur/NoInstancesException.php
+++ b/lib/Recur/NoInstancesException.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\Recur;
 
-use Exception;
-
 /**
  * This exception gets thrown when a recurrence iterator produces 0 instances.
  *
@@ -13,6 +11,6 @@
  * @author Evert Pot (http://evertpot.com/)
  * @license http://code.google.com/p/sabredav/wiki/License Modified BSD License
  */
-class NoInstancesException extends Exception
+class NoInstancesException extends \Exception
 {
 }
diff --git a/lib/Recur/RDateIterator.php b/lib/Recur/RDateIterator.php
index 5d56657fa..4ad688f9d 100644
--- a/lib/Recur/RDateIterator.php
+++ b/lib/Recur/RDateIterator.php
@@ -2,9 +2,9 @@
 
 namespace Sabre\VObject\Recur;
 
-use DateTimeInterface;
 use Iterator;
 use Sabre\VObject\DateTimeParser;
+use Sabre\VObject\InvalidDataException;
 
 /**
  * RRuleParser.
@@ -19,14 +19,14 @@
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
  */
-class RDateIterator implements Iterator
+class RDateIterator implements \Iterator
 {
     /**
      * Creates the Iterator.
      *
      * @param string|array $rrule
      */
-    public function __construct($rrule, DateTimeInterface $start)
+    public function __construct($rrule, \DateTimeInterface $start)
     {
         $this->startDate = $start;
         $this->parseRDate($rrule);
@@ -36,10 +36,10 @@ public function __construct($rrule, DateTimeInterface $start)
     /* Implementation of the Iterator interface {{{ */
 
     #[\ReturnTypeWillChange]
-    public function current()
+    public function current(): ?\DateTimeInterface
     {
         if (!$this->valid()) {
-            return;
+            return null;
         }
 
         return clone $this->currentDate;
@@ -47,11 +47,9 @@ public function current()
 
     /**
      * Returns the current item number.
-     *
-     * @return int
      */
     #[\ReturnTypeWillChange]
-    public function key()
+    public function key(): int
     {
         return $this->counter;
     }
@@ -59,22 +57,18 @@ public function key()
     /**
      * Returns whether the current item is a valid item for the recurrence
      * iterator.
-     *
-     * @return bool
      */
     #[\ReturnTypeWillChange]
-    public function valid()
+    public function valid(): bool
     {
         return $this->counter <= count($this->dates);
     }
 
     /**
      * Resets the iterator.
-     *
-     * @return void
      */
     #[\ReturnTypeWillChange]
-    public function rewind()
+    public function rewind(): void
     {
         $this->currentDate = clone $this->startDate;
         $this->counter = 0;
@@ -83,10 +77,10 @@ public function rewind()
     /**
      * Goes on to the next iteration.
      *
-     * @return void
+     * @throws InvalidDataException
      */
     #[\ReturnTypeWillChange]
-    public function next()
+    public function next(): void
     {
         ++$this->counter;
         if (!$this->valid()) {
@@ -104,10 +98,8 @@ public function next()
 
     /**
      * Returns true if this recurring event never ends.
-     *
-     * @return bool
      */
-    public function isInfinite()
+    public function isInfinite(): bool
     {
         return false;
     }
@@ -115,8 +107,10 @@ public function isInfinite()
     /**
      * This method allows you to quickly go to the next occurrence after the
      * specified date.
+     *
+     * @throws InvalidDataException
      */
-    public function fastForward(DateTimeInterface $dt)
+    public function fastForward(\DateTimeInterface $dt): void
     {
         while ($this->valid() && $this->currentDate < $dt) {
             $this->next();
@@ -127,27 +121,21 @@ public function fastForward(DateTimeInterface $dt)
      * The reference start date/time for the rrule.
      *
      * All calculations are based on this initial date.
-     *
-     * @var DateTimeInterface
      */
-    protected $startDate;
+    protected \DateTimeInterface $startDate;
 
     /**
      * The date of the current iteration. You can get this by calling
      * ->current().
-     *
-     * @var DateTimeInterface
      */
-    protected $currentDate;
+    protected \DateTimeInterface $currentDate;
 
     /**
      * The current item in the list.
      *
      * You can get this number with the key() method.
-     *
-     * @var int
      */
-    protected $counter = 0;
+    protected int $counter = 0;
 
     /* }}} */
 
@@ -155,9 +143,9 @@ public function fastForward(DateTimeInterface $dt)
      * This method receives a string from an RRULE property, and populates this
      * class with all the values.
      *
-     * @param string|array $rrule
+     * @param string|array $rdate
      */
-    protected function parseRDate($rdate)
+    protected function parseRDate($rdate): void
     {
         if (is_string($rdate)) {
             $rdate = explode(',', $rdate);
@@ -168,8 +156,6 @@ protected function parseRDate($rdate)
 
     /**
      * Array with the RRULE dates.
-     *
-     * @var array
      */
-    protected $dates = [];
+    protected array $dates = [];
 }
diff --git a/lib/Recur/RRuleIterator.php b/lib/Recur/RRuleIterator.php
index d09838398..0b3140bb0 100644
--- a/lib/Recur/RRuleIterator.php
+++ b/lib/Recur/RRuleIterator.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\Recur;
 
-use DateTimeInterface;
-use Iterator;
 use Sabre\VObject\DateTimeParser;
 use Sabre\VObject\InvalidDataException;
 use Sabre\VObject\Property;
@@ -21,14 +19,23 @@
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
  */
-class RRuleIterator implements Iterator
+class RRuleIterator implements \Iterator
 {
+    /**
+     * Constant denoting the upper limit on how long into the future
+     * we want to iterate. The value is a unix timestamp and currently
+     * corresponds to the datetime 9999-12-31 11:59:59 UTC.
+     */
+    public const dateUpperLimit = 253402300799;
+
     /**
      * Creates the Iterator.
      *
      * @param string|array $rrule
+     *
+     * @throws InvalidDataException
      */
-    public function __construct($rrule, DateTimeInterface $start)
+    public function __construct($rrule, \DateTimeInterface $start)
     {
         $this->startDate = $start;
         $this->parseRRule($rrule);
@@ -38,10 +45,10 @@ public function __construct($rrule, DateTimeInterface $start)
     /* Implementation of the Iterator interface {{{ */
 
     #[\ReturnTypeWillChange]
-    public function current()
+    public function current(): ?\DateTimeInterface
     {
         if (!$this->valid()) {
-            return;
+            return null;
         }
 
         return clone $this->currentDate;
@@ -49,24 +56,20 @@ public function current()
 
     /**
      * Returns the current item number.
-     *
-     * @return int
      */
     #[\ReturnTypeWillChange]
-    public function key()
+    public function key(): int
     {
-        return $this->counter;
+        return (int) $this->counter;
     }
 
     /**
      * Returns whether the current item is a valid item for the recurrence
      * iterator. This will return false if we've gone beyond the UNTIL or COUNT
      * statements.
-     *
-     * @return bool
      */
     #[\ReturnTypeWillChange]
-    public function valid()
+    public function valid(): bool
     {
         if (null === $this->currentDate) {
             return false;
@@ -80,11 +83,9 @@ public function valid()
 
     /**
      * Resets the iterator.
-     *
-     * @return void
      */
     #[\ReturnTypeWillChange]
-    public function rewind()
+    public function rewind(): void
     {
         $this->currentDate = clone $this->startDate;
         $this->counter = 0;
@@ -92,12 +93,9 @@ public function rewind()
 
     /**
      * Goes on to the next iteration.
-     *
-     * @param int $amount
-     * @return void
      */
     #[\ReturnTypeWillChange]
-    public function next(int $amount = 1)
+    public function next(int $amount = 1): void
     {
         // Otherwise, we find the next event in the normal RRULE
         // sequence.
@@ -125,10 +123,8 @@ public function next(int $amount = 1)
 
     /**
      * Returns true if this recurring event never ends.
-     *
-     * @return bool
      */
-    public function isInfinite()
+    public function isInfinite(): bool
     {
         return !$this->count && !$this->until;
     }
@@ -137,7 +133,7 @@ public function isInfinite()
      * This method allows you to quickly go to the next occurrence after the
      * specified date.
      */
-    public function fastForward(DateTimeInterface $dt)
+    public function fastForward(\DateTimeInterface $dt): void
     {
         // We don't do any jumps if we have a count limit as we have to keep track of the number of occurrences
         if (!isset($this->count)) {
@@ -152,7 +148,7 @@ public function fastForward(DateTimeInterface $dt)
     /**
      * This method allows you to quickly go to the next occurrence before the specified date.
      */
-    public function fastForwardBefore(DateTimeInterface $dt)
+    public function fastForwardBefore(\DateTimeInterface $dt): void
     {
         $hasCount = isset($this->count);
 
@@ -176,7 +172,7 @@ public function fastForwardBefore(DateTimeInterface $dt)
     /**
      * This method allows you to quickly go to the last occurrence.
      */
-    public function fastForwardToEnd()
+    public function fastForwardToEnd(): void
     {
         if ($this->isInfinite()) {
             throw new \LogicException('Cannot fast forward to the end an infinite event.');
@@ -199,22 +195,22 @@ public function fastForwardToEnd()
         $this->currentDate = $previous;
     }
 
-    public function getCount()
+    public function getCount(): ?int
     {
         return $this->count;
     }
 
-    public function getInterval()
+    public function getInterval(): int
     {
         return $this->interval;
     }
 
-    public function getUntil()
+    public function getUntil(): ?\DateTimeInterface
     {
         return $this->until;
     }
 
-    public function getFrequency()
+    public function getFrequency(): string
     {
         return $this->frequency;
     }
@@ -254,7 +250,7 @@ private function getFrequencyCoeff()
      * recurrence rule. Will set the position of the iterator to the last occurrence before the requested date. If the
      * fast forwarding failed, the position will be reset.
      */
-    private function jumpForward(DateTimeInterface $dt)
+    private function jumpForward(\DateTimeInterface $dt): void
     {
         $frequencyCoeff = $this->getFrequencyCoeff();
 
@@ -302,86 +298,66 @@ private function jumpForward(DateTimeInterface $dt)
      * The reference start date/time for the rrule.
      *
      * All calculations are based on this initial date.
-     *
-     * @var DateTimeInterface
      */
-    protected $startDate;
+    protected \DateTimeInterface $startDate;
 
     /**
      * The date of the current iteration. You can get this by calling
      * ->current().
-     *
-     * @var DateTimeInterface
      */
-    protected $currentDate;
+    protected ?\DateTimeInterface $currentDate;
 
     /**
      * Frequency is one of: secondly, minutely, hourly, daily, weekly, monthly,
      * yearly.
-     *
-     * @var string
      */
-    protected $frequency;
+    protected string $frequency;
 
     /**
      * The number of recurrences, or 'null' if infinitely recurring.
-     *
-     * @var int
      */
-    protected $count;
+    protected ?int $count = null;
 
     /**
      * The interval.
      *
      * If for example frequency is set to daily, interval = 2 would mean every
      * 2 days.
-     *
-     * @var int
      */
-    protected $interval = 1;
+    protected int $interval = 1;
 
     /**
      * The last instance of this recurrence, inclusively.
-     *
-     * @var DateTimeInterface|null
      */
-    protected $until;
+    protected ?\DateTimeInterface $until = null;
 
     /**
      * Which seconds to recur.
      *
      * This is an array of integers (between 0 and 60)
-     *
-     * @var array
      */
-    protected $bySecond;
+    protected ?array $bySecond = null;
 
     /**
      * Which minutes to recur.
      *
      * This is an array of integers (between 0 and 59)
-     *
-     * @var array
      */
-    protected $byMinute;
+    protected ?array $byMinute = null;
 
     /**
      * Which hours to recur.
      *
      * This is an array of integers (between 0 and 23)
-     *
-     * @var array
      */
-    protected $byHour;
+    protected ?array $byHour = null;
 
     /**
      * The current item in the list.
      *
      * You can get this number with the key() method.
-     *
-     * @var int
      */
-    protected $counter = 0;
+    protected float $counter = 0;
 
     /**
      * Which weekdays to recur.
@@ -392,20 +368,16 @@ private function jumpForward(DateTimeInterface $dt)
      * this indicates the nth occurrence of a specific day within the monthly or
      * yearly rrule. For instance, -2TU indicates the second-last tuesday of
      * the month, or year.
-     *
-     * @var array
      */
-    protected $byDay;
+    protected ?array $byDay = null;
 
     /**
      * Which days of the month to recur.
      *
      * This is an array of days of the months (1-31). The value can also be
      * negative. -5 for instance means the 5th last day of the month.
-     *
-     * @var array
      */
-    protected $byMonthDay;
+    protected ?array $byMonthDay = null;
 
     /**
      * Which days of the year to recur.
@@ -413,29 +385,23 @@ private function jumpForward(DateTimeInterface $dt)
      * This is an array with days of the year (1 to 366). The values can also
      * be negative. For instance, -1 will always represent the last day of the
      * year. (December 31st).
-     *
-     * @var array
      */
-    protected $byYearDay;
+    protected ?array $byYearDay = null;
 
     /**
      * Which week numbers to recur.
      *
      * This is an array of integers from 1 to 53. The values can also be
      * negative. -1 will always refer to the last week of the year.
-     *
-     * @var array
      */
-    protected $byWeekNo;
+    protected ?array $byWeekNo = null;
 
     /**
      * Which months to recur.
      *
      * This is an array of integers from 1 to 12.
-     *
-     * @var array
      */
-    protected $byMonth;
+    protected ?array $byMonth = null;
 
     /**
      * Which items in an existing st to recur.
@@ -448,24 +414,20 @@ private function jumpForward(DateTimeInterface $dt)
      *
      * This would be done by setting frequency to 'monthly', byDay to
      * 'MO,TU,WE,TH,FR' and bySetPos to -1.
-     *
-     * @var array
      */
-    protected $bySetPos;
+    protected ?array $bySetPos = null;
 
     /**
      * When the week starts.
-     *
-     * @var string
      */
-    protected $weekStart = 'MO';
+    protected string $weekStart = 'MO';
 
     /* Functions that advance the iterator {{{ */
 
     /**
      * Does the processing for advancing the iterator for hourly frequency.
      */
-    protected function nextHourly($amount = 1)
+    protected function nextHourly($amount = 1): void
     {
         $this->currentDate = $this->currentDate->modify('+'.$amount * $this->interval.' hours');
     }
@@ -473,7 +435,7 @@ protected function nextHourly($amount = 1)
     /**
      * Does the processing for advancing the iterator for daily frequency.
      */
-    protected function nextDaily($amount = 1)
+    protected function nextDaily($amount = 1): void
     {
         if (!$this->byHour && !$this->byDay) {
             $this->currentDate = $this->currentDate->modify('+'.$amount * $this->interval.' days');
@@ -518,17 +480,23 @@ protected function nextDaily($amount = 1)
 
             // Current hour of the day
             $currentHour = $this->currentDate->format('G');
+
+            if ($this->currentDate->getTimestamp() > self::dateUpperLimit) {
+                $this->currentDate = null;
+
+                return;
+            }
         } while (
-            ($this->byDay && !in_array($currentDay, $recurrenceDays)) ||
-            ($this->byHour && !in_array($currentHour, $recurrenceHours)) ||
-            ($this->byMonth && !in_array($currentMonth, $recurrenceMonths))
+            ($this->byDay && !in_array($currentDay, $recurrenceDays))
+            || ($this->byHour && !in_array($currentHour, $recurrenceHours))
+            || ($this->byMonth && !in_array($currentMonth, $recurrenceMonths))
         );
     }
 
     /**
      * Does the processing for advancing the iterator for weekly frequency.
      */
-    protected function nextWeekly($amount = 1)
+    protected function nextWeekly($amount = 1): void
     {
         if (!$this->byHour && !$this->byDay) {
             $this->currentDate = $this->currentDate->modify('+'.($amount * $this->interval).' weeks');
@@ -579,8 +547,10 @@ protected function nextWeekly($amount = 1)
 
     /**
      * Does the processing for advancing the iterator for monthly frequency.
+     *
+     * @throws \Exception
      */
-    protected function nextMonthly($amount = 1)
+    protected function nextMonthly($amount = 1): void
     {
         $currentDayOfMonth = $this->currentDate->format('j');
         $currentHourOfMonth = $this->currentDate->format('G');
@@ -648,9 +618,6 @@ protected function nextMonthly($amount = 1)
             // This goes to 0 because we need to start counting at the
             // beginning.
             $currentDayOfMonth = 0;
-
-            // For some reason the "until" parameter was not being used here,
-            // that's why the workaround of the 10000 year bug was needed at all
             $currentHourOfMonth = 0;
             $currentMinuteOfMonth = 0;
             $currentSecondOfMonth = 0;
@@ -661,14 +628,10 @@ protected function nextMonthly($amount = 1)
             if ($this->until && $this->currentDate->getTimestamp() >= $this->until->getTimestamp()) {
                 return;
             }
-            // let's stop it before the "until" parameter date
-            if ($this->until && $this->currentDate->getTimestamp() >= $this->until->getTimestamp()) {
-                return;
-            }
 
             // To prevent running this forever (better: until we hit the max date of DateTimeImmutable) we simply
             // stop at 9999-12-31. Looks like the year 10000 problem is not solved in php ....
-            if ($this->currentDate->getTimestamp() > 253402300799) {
+            if ($this->currentDate->getTimestamp() > self::dateUpperLimit) {
                 $this->currentDate = null;
 
                 return;
@@ -685,7 +648,7 @@ protected function nextMonthly($amount = 1)
     /**
      * Does the processing for advancing the iterator for yearly frequency.
      */
-    protected function nextYearly($amount = 1)
+    protected function nextYearly($amount = 1): void
     {
         $currentYear = $this->currentDate->format('Y');
         $currentMonth = $this->currentDate->format('n');
@@ -897,8 +860,10 @@ protected function nextYearly($amount = 1)
      * class with all the values.
      *
      * @param string|array $rrule
+     *
+     * @throws InvalidDataException
      */
-    protected function parseRRule($rrule)
+    protected function parseRRule($rrule): void
     {
         if (is_string($rrule)) {
             $rrule = Property\ICalendar\Recur::stringToArray($rrule);
@@ -1029,9 +994,9 @@ protected function parseRRule($rrule)
         }
 
         if (
-            (isset($this->byWeekNo) && $this->frequency !== 'yearly') ||
-            (isset($this->byYearDay) && in_array($this->frequency, ['daily', 'weekly', 'monthly'], true)) ||
-            (isset($this->byMonthDay) && $this->frequency === 'weekly')
+            (isset($this->byWeekNo) && 'yearly' !== $this->frequency)
+            || (isset($this->byYearDay) && in_array($this->frequency, ['daily', 'weekly', 'monthly'], true))
+            || (isset($this->byMonthDay) && 'weekly' === $this->frequency)
         ) {
             throw new InvalidDataException('Invalid combination of FREQ with BY rules');
         }
@@ -1039,10 +1004,8 @@ protected function parseRRule($rrule)
 
     /**
      * Mappings between the day number and english day name.
-     *
-     * @var array
      */
-    protected $dayNames = [
+    protected array $dayNames = [
         0 => 'Sunday',
         1 => 'Monday',
         2 => 'Tuesday',
@@ -1059,9 +1022,9 @@ protected function parseRRule($rrule)
      * The returned list is an array of arrays with as first element the day of month (1-31);
      *  the hour; the minute and second of the occurence
      *
-     * @return array
+     * @throws \Exception
      */
-    protected function getMonthlyOccurrences()
+    protected function getMonthlyOccurrences(): array
     {
         $startDate = clone $this->currentDate;
 
@@ -1110,7 +1073,7 @@ protected function getMonthlyOccurrences()
                     }
                 } else {
                     // There was no counter (first, second, last wednesdays), so we
-                    // just need to add the all to the list).
+                    // just need to add the all to the list.
                     $byDayResults = array_merge($byDayResults, $dayHits);
                 }
             }
@@ -1120,8 +1083,8 @@ protected function getMonthlyOccurrences()
         if ($this->byMonthDay) {
             foreach ($this->byMonthDay as $monthDay) {
                 // Removing values that are out of range for this month
-                if ($monthDay > $startDate->format('t') ||
-                    $monthDay < 0 - $startDate->format('t')) {
+                if ($monthDay > $startDate->format('t')
+                    || $monthDay < 0 - $startDate->format('t')) {
                     continue;
                 }
                 if ($monthDay > 0) {
@@ -1189,7 +1152,7 @@ protected function getMonthlyOccurrences()
      *
      * @return array an array of arrays with the day of the month, hours, minute and seconds of the occurence
      */
-    protected function addDailyOccurences(array $result)
+    protected function addDailyOccurences(array $result): array
     {
         $output = [];
         $hour = (int) $this->currentDate->format('G');
@@ -1213,10 +1176,8 @@ protected function addDailyOccurences(array $result)
 
     /**
      * Simple mapping from iCalendar day names to day numbers.
-     *
-     * @var array
      */
-    protected $dayMap = [
+    protected array $dayMap = [
         'SU' => 0,
         'MO' => 1,
         'TU' => 2,
@@ -1226,7 +1187,7 @@ protected function addDailyOccurences(array $result)
         'SA' => 6,
     ];
 
-    protected function getHours()
+    protected function getHours(): array
     {
         $recurrenceHours = [];
         foreach ($this->byHour as $byHour) {
@@ -1236,7 +1197,7 @@ protected function getHours()
         return $recurrenceHours;
     }
 
-    protected function getDays()
+    protected function getDays(): array
     {
         $recurrenceDays = [];
         foreach ($this->byDay as $byDay) {
@@ -1249,7 +1210,7 @@ protected function getDays()
         return $recurrenceDays;
     }
 
-    protected function getMonths()
+    protected function getMonths(): array
     {
         $recurrenceMonths = [];
         foreach ($this->byMonth as $byMonth) {
diff --git a/lib/Settings.php b/lib/Settings.php
index b0bb80a82..5e50f914f 100644
--- a/lib/Settings.php
+++ b/lib/Settings.php
@@ -25,7 +25,7 @@ class Settings
      * use-cases. In particular, it covers birthdates for virtually everyone
      * alive on earth, which is less than 5 people at the time of writing.
      */
-    public static $minDate = '1900-01-01';
+    public static string $minDate = '1900-01-01';
 
     /**
      * The maximum date we accept for various calculations with dates, such as
@@ -34,7 +34,7 @@ class Settings
      * The choice of 2100 is pretty arbitrary, but should cover most
      * appointments made for many years to come.
      */
-    public static $maxDate = '2100-01-01';
+    public static string $maxDate = '2100-01-01';
 
     /**
      * The maximum number of recurrences that will be generated.
@@ -51,5 +51,5 @@ class Settings
      *
      * Set this value to -1 to disable this control altogether.
      */
-    public static $maxRecurrences = 3500;
+    public static int $maxRecurrences = 3500;
 }
diff --git a/lib/Splitter/ICalendar.php b/lib/Splitter/ICalendar.php
index d42566194..ccf0d1add 100644
--- a/lib/Splitter/ICalendar.php
+++ b/lib/Splitter/ICalendar.php
@@ -3,6 +3,7 @@
 namespace Sabre\VObject\Splitter;
 
 use Sabre\VObject;
+use Sabre\VObject\Component;
 use Sabre\VObject\Component\VCalendar;
 
 /**
@@ -23,27 +24,25 @@ class ICalendar implements SplitterInterface
 {
     /**
      * Timezones.
-     *
-     * @var array
      */
-    protected $vtimezones = [];
+    protected array $vtimezones = [];
 
     /**
      * iCalendar objects.
-     *
-     * @var array
      */
-    protected $objects = [];
+    protected array $objects = [];
 
     /**
      * Constructor.
      *
-     * The splitter should receive an readable file stream as its input.
+     * The splitter should receive a readable file stream as its input.
      *
      * @param resource $input
      * @param int      $options parser options, see the OPTIONS constants
+     *
+     * @throws VObject\ParseException
      */
-    public function __construct($input, $options = 0)
+    public function __construct($input, int $options = 0)
     {
         $data = VObject\Reader::read($input, $options);
 
@@ -52,7 +51,7 @@ public function __construct($input, $options = 0)
         }
 
         foreach ($data->children() as $component) {
-            if (!$component instanceof VObject\Component) {
+            if (!$component instanceof Component) {
                 continue;
             }
 
@@ -82,10 +81,8 @@ public function __construct($input, $options = 0)
      * hit the end of the stream.
      *
      * When the end is reached, null will be returned.
-     *
-     * @return \Sabre\VObject\Component|null
      */
-    public function getNext()
+    public function getNext(): ?Component
     {
         if ($object = array_shift($this->objects)) {
             // create our baseobject
@@ -100,7 +97,7 @@ public function getNext()
 
             return $object;
         } else {
-            return;
+            return null;
         }
     }
 }
diff --git a/lib/Splitter/SplitterInterface.php b/lib/Splitter/SplitterInterface.php
index c845ac5fc..c4014abf3 100644
--- a/lib/Splitter/SplitterInterface.php
+++ b/lib/Splitter/SplitterInterface.php
@@ -2,6 +2,8 @@
 
 namespace Sabre\VObject\Splitter;
 
+use Sabre\VObject\Component;
+
 /**
  * VObject splitter.
  *
@@ -20,7 +22,7 @@ interface SplitterInterface
     /**
      * Constructor.
      *
-     * The splitter should receive an readable file stream as its input.
+     * The splitter should receive a readable file stream as its input.
      *
      * @param resource $input
      */
@@ -31,8 +33,6 @@ public function __construct($input);
      * hit the end of the stream.
      *
      * When the end is reached, null will be returned.
-     *
-     * @return \Sabre\VObject\Component|null
      */
-    public function getNext();
+    public function getNext(): ?Component;
 }
diff --git a/lib/Splitter/VCard.php b/lib/Splitter/VCard.php
index a20f5c2c1..e63ae837d 100644
--- a/lib/Splitter/VCard.php
+++ b/lib/Splitter/VCard.php
@@ -3,6 +3,7 @@
 namespace Sabre\VObject\Splitter;
 
 use Sabre\VObject;
+use Sabre\VObject\Component;
 use Sabre\VObject\Parser\MimeDir;
 
 /**
@@ -30,20 +31,18 @@ class VCard implements SplitterInterface
 
     /**
      * Persistent parser.
-     *
-     * @var MimeDir
      */
-    protected $parser;
+    protected MimeDir $parser;
 
     /**
      * Constructor.
      *
-     * The splitter should receive an readable file stream as its input.
+     * The splitter should receive a readable file stream as its input.
      *
      * @param resource $input
      * @param int      $options parser options, see the OPTIONS constants
      */
-    public function __construct($input, $options = 0)
+    public function __construct($input, int $options = 0)
     {
         $this->input = $input;
         $this->parser = new MimeDir($input, $options);
@@ -55,9 +54,9 @@ public function __construct($input, $options = 0)
      *
      * When the end is reached, null will be returned.
      *
-     * @return \Sabre\VObject\Component|null
+     * @throws VObject\ParseException
      */
-    public function getNext()
+    public function getNext(): ?Component
     {
         try {
             $object = $this->parser->parse();
@@ -66,7 +65,7 @@ public function getNext()
                 throw new VObject\ParseException('The supplied input contained non-VCARD data.');
             }
         } catch (VObject\EofException $e) {
-            return;
+            return null;
         }
 
         return $object;
diff --git a/lib/StringUtil.php b/lib/StringUtil.php
index 2333d6ab9..8fe5f9f0a 100644
--- a/lib/StringUtil.php
+++ b/lib/StringUtil.php
@@ -13,12 +13,8 @@ class StringUtil
 {
     /**
      * Returns true or false depending on if a string is valid UTF-8.
-     *
-     * @param string $str
-     *
-     * @return bool
      */
-    public static function isUTF8($str)
+    public static function isUTF8(string $str): bool
     {
         // Control characters
         if (preg_match('%[\x00-\x08\x0B-\x0C\x0E\x0F]%', $str)) {
@@ -33,30 +29,14 @@ public static function isUTF8($str)
      *
      * Currently only ISO-5991-1 input and UTF-8 input is supported, but this
      * may be expanded upon if we receive other examples.
-     *
-     * @param string $str
-     *
-     * @return string
      */
-    public static function convertToUTF8($str)
+    public static function convertToUTF8(string $str): string
     {
-        $encoding = mb_detect_encoding($str, ['UTF-8', 'ISO-8859-1', 'WINDOWS-1252'], true);
-
-        switch ($encoding) {
-            case 'ISO-8859-1':
-                $newStr = utf8_encode($str);
-                break;
-            /* Unreachable code. Not sure yet how we can improve this
-             * situation.
-            case 'WINDOWS-1252' :
-                $newStr = iconv('cp1252', 'UTF-8', $str);
-                break;
-             */
-            default:
-                 $newStr = $str;
+        if (!mb_check_encoding($str, 'UTF-8') && mb_check_encoding($str, 'ISO-8859-1')) {
+            $str = mb_convert_encoding($str, 'UTF-8', 'ISO-8859-1');
         }
 
         // Removing any control characters
-        return preg_replace('%(?:[\x00-\x08\x0B-\x0C\x0E-\x1F\x7F])%', '', $newStr);
+        return preg_replace('%(?:[\x00-\x08\x0B-\x0C\x0E-\x1F\x7F])%', '', $str);
     }
 }
diff --git a/lib/TimeZoneUtil.php b/lib/TimeZoneUtil.php
index 3d9885b0d..79a5920af 100644
--- a/lib/TimeZoneUtil.php
+++ b/lib/TimeZoneUtil.php
@@ -2,17 +2,15 @@
 
 namespace Sabre\VObject;
 
-use DateTimeZone;
-use InvalidArgumentException;
 use Sabre\VObject\TimezoneGuesser\FindFromMzVersionTimezone;
 use Sabre\VObject\TimezoneGuesser\FindFromOffset;
 use Sabre\VObject\TimezoneGuesser\FindFromOffsetName;
 use Sabre\VObject\TimezoneGuesser\FindFromOutlookCities;
 use Sabre\VObject\TimezoneGuesser\FindFromTimezoneIdentifier;
 use Sabre\VObject\TimezoneGuesser\FindFromTimezoneMap;
+use Sabre\VObject\TimezoneGuesser\GuessFromCustomizedTimeZone;
 use Sabre\VObject\TimezoneGuesser\GuessFromLicEntry;
 use Sabre\VObject\TimezoneGuesser\GuessFromMsTzId;
-use Sabre\VObject\TimezoneGuesser\GuessFromCustomizedTimeZone;
 use Sabre\VObject\TimezoneGuesser\LowercaseTimezoneIdentifier;
 use Sabre\VObject\TimezoneGuesser\TimezoneFinder;
 use Sabre\VObject\TimezoneGuesser\TimezoneGuesser;
@@ -29,14 +27,13 @@
  */
 class TimeZoneUtil
 {
-    /** @var self */
-    private static $instance = null;
+    private static ?TimeZoneUtil $instance = null;
 
     /** @var TimezoneGuesser[] */
-    private $timezoneGuessers = [];
+    private array $timezoneGuessers = [];
 
     /** @var TimezoneFinder[] */
-    private $timezoneFinders = [];
+    private array $timezoneFinders = [];
 
     private function __construct()
     {
@@ -84,11 +81,11 @@ private function addFinder(string $key, TimezoneFinder $finder): void
      * Alternatively, if $failIfUncertain is set to true, it will throw an
      * exception if we cannot accurately determine the timezone.
      */
-    private function findTimeZone(string $tzid, Component $vcalendar = null, bool $failIfUncertain = false, bool $activeCustomizedGuesser = false): DateTimeZone
+    private function findTimeZone(string $tzid, Component $vcalendar = null, bool $failIfUncertain = false, bool $activeCustomizedGuesser = false): \DateTimeZone
     {
         foreach ($this->timezoneFinders as $timezoneFinder) {
             $timezone = $timezoneFinder->find($tzid, $failIfUncertain);
-            if (!$timezone instanceof DateTimeZone) {
+            if (!$timezone instanceof \DateTimeZone) {
                 continue;
             }
 
@@ -111,7 +108,7 @@ private function findTimeZone(string $tzid, Component $vcalendar = null, bool $f
                 if ((string) $vtimezone->TZID === $tzid) {
                     foreach ($guessers as $timezoneGuesser) {
                         $timezone = $timezoneGuesser->guess($vtimezone, $failIfUncertain);
-                        if (!$timezone instanceof DateTimeZone) {
+                        if (!$timezone instanceof \DateTimeZone) {
                             continue;
                         }
 
@@ -122,11 +119,11 @@ private function findTimeZone(string $tzid, Component $vcalendar = null, bool $f
         }
 
         if ($failIfUncertain) {
-            throw new InvalidArgumentException('We were unable to determine the correct PHP timezone for tzid: '.$tzid);
+            throw new \InvalidArgumentException('We were unable to determine the correct PHP timezone for tzid: '.$tzid);
         }
 
         // If we got all the way here, we default to whatever has been set as the PHP default timezone.
-        return new DateTimeZone(date_default_timezone_get());
+        return new \DateTimeZone(date_default_timezone_get());
     }
 
     public static function addTimezoneGuesser(string $key, TimezoneGuesser $guesser): void
@@ -139,13 +136,7 @@ public static function addTimezoneFinder(string $key, TimezoneFinder $finder): v
         self::getInstance()->addFinder($key, $finder);
     }
 
-    /**
-     * @param string $tzid
-     * @param false  $failIfUncertain
-     *
-     * @return DateTimeZone
-     */
-    public static function getTimeZone($tzid, Component $vcalendar = null, $failIfUncertain = false, bool $activeCustomizedGuesser = true)
+    public static function getTimeZone(string $tzid, Component $vcalendar = null, bool $failIfUncertain = false, bool $activeCustomizedGuesser = true): \DateTimeZone
     {
         return self::getInstance()->findTimeZone($tzid, $vcalendar, $failIfUncertain, $activeCustomizedGuesser);
     }
@@ -154,139 +145,4 @@ public static function clean(): void
     {
         self::$instance = null;
     }
-
-    // Keeping things for backwards compatibility
-    /**
-     * @var array|null
-     *
-     * @deprecated
-     */
-    public static $map = null;
-
-    /**
-     * List of microsoft exchange timezone ids.
-     *
-     * Source: http://msdn.microsoft.com/en-us/library/aa563018(loband).aspx
-     *
-     * @deprecated
-     */
-    public static $microsoftExchangeMap = [
-        0 => 'UTC',
-        31 => 'Africa/Casablanca',
-        // Insanely, id #2 is used for both Europe/Lisbon, and Europe/Sarajevo.
-        // I'm not even kidding.. We handle this special case in the
-        // getTimeZone method.
-        2 => 'Europe/Lisbon',
-        1 => 'Europe/London',
-        4 => 'Europe/Berlin',
-        6 => 'Europe/Prague',
-        3 => 'Europe/Paris',
-        69 => 'Africa/Luanda', // This was a best guess
-        7 => 'Europe/Athens',
-        5 => 'Europe/Bucharest',
-        49 => 'Africa/Cairo',
-        50 => 'Africa/Harare',
-        59 => 'Europe/Helsinki',
-        27 => 'Asia/Jerusalem',
-        26 => 'Asia/Baghdad',
-        74 => 'Asia/Kuwait',
-        51 => 'Europe/Moscow',
-        56 => 'Africa/Nairobi',
-        25 => 'Asia/Tehran',
-        24 => 'Asia/Muscat', // Best guess
-        54 => 'Asia/Baku',
-        48 => 'Asia/Kabul',
-        58 => 'Asia/Yekaterinburg',
-        47 => 'Asia/Karachi',
-        23 => 'Asia/Calcutta',
-        62 => 'Asia/Kathmandu',
-        46 => 'Asia/Almaty',
-        71 => 'Asia/Dhaka',
-        66 => 'Asia/Colombo',
-        61 => 'Asia/Rangoon',
-        22 => 'Asia/Bangkok',
-        64 => 'Asia/Krasnoyarsk',
-        45 => 'Asia/Shanghai',
-        63 => 'Asia/Irkutsk',
-        21 => 'Asia/Singapore',
-        73 => 'Australia/Perth',
-        75 => 'Asia/Taipei',
-        20 => 'Asia/Tokyo',
-        72 => 'Asia/Seoul',
-        70 => 'Asia/Yakutsk',
-        19 => 'Australia/Adelaide',
-        44 => 'Australia/Darwin',
-        18 => 'Australia/Brisbane',
-        76 => 'Australia/Sydney',
-        43 => 'Pacific/Guam',
-        42 => 'Australia/Hobart',
-        68 => 'Asia/Vladivostok',
-        41 => 'Asia/Magadan',
-        17 => 'Pacific/Auckland',
-        40 => 'Pacific/Fiji',
-        67 => 'Pacific/Tongatapu',
-        29 => 'Atlantic/Azores',
-        53 => 'Atlantic/Cape_Verde',
-        30 => 'America/Noronha',
-        8 => 'America/Sao_Paulo', // Best guess
-        32 => 'America/Argentina/Buenos_Aires',
-        60 => 'America/Godthab',
-        28 => 'America/St_Johns',
-        9 => 'America/Halifax',
-        33 => 'America/Caracas',
-        65 => 'America/Santiago',
-        35 => 'America/Bogota',
-        10 => 'America/New_York',
-        34 => 'America/Indiana/Indianapolis',
-        55 => 'America/Guatemala',
-        11 => 'America/Chicago',
-        37 => 'America/Mexico_City',
-        36 => 'America/Edmonton',
-        38 => 'America/Phoenix',
-        12 => 'America/Denver', // Best guess
-        13 => 'America/Los_Angeles', // Best guess
-        14 => 'America/Anchorage',
-        15 => 'Pacific/Honolulu',
-        16 => 'Pacific/Midway',
-        39 => 'Pacific/Kwajalein',
-    ];
-
-    /**
-     * This method will load in all the tz mapping information, if it's not yet
-     * done.
-     *
-     * @deprecated
-     */
-    public static function loadTzMaps()
-    {
-        if (!is_null(self::$map)) {
-            return;
-        }
-
-        self::$map = array_merge(
-            include __DIR__.'/timezonedata/windowszones.php',
-            include __DIR__.'/timezonedata/lotuszones.php',
-            include __DIR__.'/timezonedata/exchangezones.php',
-            include __DIR__.'/timezonedata/php-workaround.php',
-            include __DIR__.'/timezonedata/extrazones.php'
-        );
-    }
-
-    /**
-     * This method returns an array of timezone identifiers, that are supported
-     * by DateTimeZone(), but not returned by DateTimeZone::listIdentifiers().
-     *
-     * We're not using DateTimeZone::listIdentifiers(DateTimeZone::ALL_WITH_BC) because:
-     * - It's not supported by some PHP versions as well as HHVM.
-     * - It also returns identifiers, that are invalid values for new DateTimeZone() on some PHP versions.
-     * (See timezonedata/php-bc.php and timezonedata php-workaround.php)
-     *
-     * @return array
-     *
-     * @deprecated
-     */
-    public static function getIdentifiersBC()
-    {
-        return include __DIR__.'/timezonedata/php-bc.php';
-    }
 }
diff --git a/lib/TimezoneGuesser/FindFromMzVersionTimezone.php b/lib/TimezoneGuesser/FindFromMzVersionTimezone.php
index b6290288f..5abdc1484 100644
--- a/lib/TimezoneGuesser/FindFromMzVersionTimezone.php
+++ b/lib/TimezoneGuesser/FindFromMzVersionTimezone.php
@@ -4,7 +4,6 @@
 
 namespace Sabre\VObject\TimezoneGuesser;
 
-use DateTimeZone;
 use Sabre\VObject\TimeZoneUtil;
 
 /**
@@ -14,21 +13,21 @@
  */
 class FindFromMzVersionTimezone implements TimezoneFinder
 {
-    public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
+    public function find(string $tzid, ?bool $failIfUncertain = false): ?\DateTimeZone
     {
         if (strlen($tzid) < 1) {
             return null;
         }
 
-        $trailingChar = (int) $tzid[strlen($tzid)-1];
+        $trailingChar = (int) $tzid[strlen($tzid) - 1];
         if ($trailingChar <= 9 && $trailingChar >= 1) {
             $emptySpace = strrpos($tzid, ' ');
-            if ($emptySpace === false) {
+            if (false === $emptySpace) {
                 return null;
             }
 
             $tz = TimeZoneUtil::getTimeZone(substr($tzid, 0, $emptySpace));
-            if ($tz->getName() === 'UTC') {
+            if ('UTC' === $tz->getName()) {
                 return null;
             }
 
diff --git a/lib/TimezoneGuesser/FindFromOffset.php b/lib/TimezoneGuesser/FindFromOffset.php
index 990ac9692..d50cb969c 100644
--- a/lib/TimezoneGuesser/FindFromOffset.php
+++ b/lib/TimezoneGuesser/FindFromOffset.php
@@ -4,14 +4,12 @@
 
 namespace Sabre\VObject\TimezoneGuesser;
 
-use DateTimeZone;
-
 /**
  * Some clients add 'X-LIC-LOCATION' with the olson name.
  */
 class FindFromOffset implements TimezoneFinder
 {
-    public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
+    public function find(string $tzid, ?bool $failIfUncertain = false): ?\DateTimeZone
     {
         // Maybe the author was hyper-lazy and just included an offset. We
         // support it, but we aren't happy about it.
@@ -22,7 +20,7 @@ public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
             // for versions under PHP 5.5.10, this bit can be taken out of the
             // source.
             // @codeCoverageIgnoreStart
-            return new DateTimeZone('Etc/GMT'.$matches[1].ltrim(substr($matches[2], 0, 2), '0'));
+            return new \DateTimeZone('Etc/GMT'.$matches[1].ltrim(substr($matches[2], 0, 2), '0'));
             // @codeCoverageIgnoreEnd
         }
 
diff --git a/lib/TimezoneGuesser/FindFromOffsetName.php b/lib/TimezoneGuesser/FindFromOffsetName.php
index 73a9eab34..0916f1283 100644
--- a/lib/TimezoneGuesser/FindFromOffsetName.php
+++ b/lib/TimezoneGuesser/FindFromOffsetName.php
@@ -4,11 +4,9 @@
 
 namespace Sabre\VObject\TimezoneGuesser;
 
-use DateTimeZone;
-
 class FindFromOffsetName implements TimezoneFinder
 {
-    public static $offsetTimezones = [
+    public static array $offsetTimezones = [
         '+01:00' => 'Africa/Lagos',
         '+02:00' => 'Africa/Cairo',
         '+03:00' => 'Europe/Moscow',
@@ -35,7 +33,7 @@ class FindFromOffsetName implements TimezoneFinder
         '-11:00' => 'Pacific/Niue',
     ];
 
-    public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
+    public function find(string $tzid, ?bool $failIfUncertain = false): ?\DateTimeZone
     {
         // only handle number timezone
         if (strlen($tzid) > 6) {
@@ -43,9 +41,9 @@ public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
         }
 
         try {
-            $tzid = new DateTimeZone($tzid);
+            $tzid = new \DateTimeZone($tzid);
 
-            return new DateTimeZone(self::$offsetTimezones[$tzid->getName()]) ?? null;
+            return new \DateTimeZone(self::$offsetTimezones[$tzid->getName()]) ?? null;
         } catch (\Exception $e) {
             return null;
         }
diff --git a/lib/TimezoneGuesser/FindFromOutlookCities.php b/lib/TimezoneGuesser/FindFromOutlookCities.php
index 6ab672ecf..657767a37 100644
--- a/lib/TimezoneGuesser/FindFromOutlookCities.php
+++ b/lib/TimezoneGuesser/FindFromOutlookCities.php
@@ -4,17 +4,15 @@
 
 namespace Sabre\VObject\TimezoneGuesser;
 
-use DateTimeZone;
-
 class FindFromOutlookCities implements TimezoneFinder
 {
     /**
-     * Example: TZID:(UTC+01:00) Bruxelles\, København\, Madrid\, Paris
+     * Example: TZID:(UTC+01:00) Bruxelles\, København\, Madrid\, Paris.
      */
-    public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
+    public function find(string $tzid, ?bool $failIfUncertain = false): ?\DateTimeZone
     {
         $tzid = preg_replace('/TZID:\(UTC(\+|\-)\d{2}:\d{2}\)/', '', $tzid, -1, $count);
-        if ($count === 0) {
+        if (0 === $count) {
             return null;
         }
 
@@ -25,16 +23,16 @@ public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
 
         $cities = explode(', ', $tzid);
 
-        if (count($cities) === 1) {
+        if (1 === count($cities)) {
             return null;
         }
 
-        $tzIdentifiers = DateTimeZone::listIdentifiers();
+        $tzIdentifiers = \DateTimeZone::listIdentifiers();
 
         foreach ($cities as $city) {
             foreach ($tzIdentifiers as $tzIdentifier) {
                 if (str_contains(strtolower($tzIdentifier), strtolower($city))) {
-                    return new DateTimeZone($tzIdentifier);
+                    return new \DateTimeZone($tzIdentifier);
                 }
             }
         }
diff --git a/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php b/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php
index a2578bc2d..4c2c6a5a3 100644
--- a/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php
+++ b/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php
@@ -4,9 +4,6 @@
 
 namespace Sabre\VObject\TimezoneGuesser;
 
-use DateTimeZone;
-use Exception;
-
 /**
  * Some clients add 'X-LIC-LOCATION' with the olson name.
  */
@@ -16,7 +13,7 @@ class FindFromTimezoneIdentifier implements TimezoneFinder
         'Europe/Kyiv' => 'Europe/Kiev',
     ];
 
-    public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
+    public function find(string $tzid, ?bool $failIfUncertain = false): ?\DateTimeZone
     {
         // First we will just see if the tzid is a support timezone identifier.
         //
@@ -49,19 +46,19 @@ public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
         // https://bugs.php.net/bug.php?id=67881
         //
         // That's why we're checking if we'll be able to successfully instantiate
-        // \DateTimeZone() before doing so. Otherwise we could simply instantiate
+        // \DateTimeZone() before doing so. Otherwise, we could simply instantiate
         // and catch the exception.
-        $tzIdentifiers = DateTimeZone::listIdentifiers();
+        $tzIdentifiers = \DateTimeZone::listIdentifiers();
 
         try {
             if (
-                (in_array($tzid, $tzIdentifiers)) ||
-                (preg_match('/^GMT(\+|-)([0-9]{4})$/', $tzid, $matches)) ||
-                (in_array($tzid, $this->getIdentifiersBC()))
+                in_array($tzid, $tzIdentifiers)
+                || preg_match('/^GMT(\+|-)([0-9]{4})$/', $tzid, $matches)
+                || in_array($tzid, $this->getIdentifiersBC())
             ) {
-                return new DateTimeZone($tzid);
+                return new \DateTimeZone($tzid);
             }
-        } catch (Exception $e) {
+        } catch (\Exception $e) {
         }
 
         return null;
@@ -75,10 +72,8 @@ public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
      * - It's not supported by some PHP versions as well as HHVM.
      * - It also returns identifiers, that are invalid values for new DateTimeZone() on some PHP versions.
      * (See timezonedata/php-bc.php and timezonedata php-workaround.php)
-     *
-     * @return array
      */
-    private function getIdentifiersBC()
+    private function getIdentifiersBC(): array
     {
         return include __DIR__.'/../timezonedata/php-bc.php';
     }
diff --git a/lib/TimezoneGuesser/FindFromTimezoneMap.php b/lib/TimezoneGuesser/FindFromTimezoneMap.php
index 4e0a64e22..1fe680230 100644
--- a/lib/TimezoneGuesser/FindFromTimezoneMap.php
+++ b/lib/TimezoneGuesser/FindFromTimezoneMap.php
@@ -4,27 +4,25 @@
 
 namespace Sabre\VObject\TimezoneGuesser;
 
-use DateTimeZone;
-
 /**
  * Some clients add 'X-LIC-LOCATION' with the olson name.
  */
 class FindFromTimezoneMap implements TimezoneFinder
 {
-    private $map = [];
+    private array $map = [];
 
-    private $patterns = [
+    private array $patterns = [
         '/^\((UTC|GMT)(\+|\-)[\d]{2}\:[\d]{2}\) (.*)/',
         '/^\((UTC|GMT)(\+|\-)[\d]{2}\.[\d]{2}\) (.*)/',
     ];
 
-    public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
+    public function find(string $tzid, ?bool $failIfUncertain = false): ?\DateTimeZone
     {
-        $tzid = str_replace(".", "", $tzid);
+        $tzid = str_replace('.', '', $tzid);
 
         // Next, we check if the tzid is somewhere in our tzid map.
         if ($this->hasTzInMap($tzid)) {
-            return new DateTimeZone($this->getTzFromMap($tzid));
+            return new \DateTimeZone($this->getTzFromMap($tzid));
         }
 
         // Some Microsoft products prefix the offset first, so let's strip that off
@@ -36,7 +34,7 @@ public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
             }
             $tzidAlternate = $matches[3];
             if ($this->hasTzInMap($tzidAlternate)) {
-                return new DateTimeZone($this->getTzFromMap($tzidAlternate));
+                return new \DateTimeZone($this->getTzFromMap($tzidAlternate));
             }
         }
 
@@ -51,10 +49,8 @@ public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
      * - It's not supported by some PHP versions as well as HHVM.
      * - It also returns identifiers, that are invalid values for new DateTimeZone() on some PHP versions.
      * (See timezonedata/php-bc.php and timezonedata php-workaround.php)
-     *
-     * @return array
      */
-    private function getTzMaps()
+    private function getTzMaps(): array
     {
         if ([] === $this->map) {
             $map = array_merge(
@@ -65,7 +61,7 @@ private function getTzMaps()
                 include __DIR__.'/../timezonedata/extrazones.php'
             );
             $this->map = array_combine(
-                array_map(static fn (string $key) => str_replace(".", "", mb_strtolower($key, 'UTF-8')), array_keys($map)),
+                array_map(static fn (string $key) => str_replace('.', '', mb_strtolower($key, 'UTF-8')), array_keys($map)),
                 array_values($map),
             );
         }
diff --git a/lib/TimezoneGuesser/GuessFromCustomizedTimeZone.php b/lib/TimezoneGuesser/GuessFromCustomizedTimeZone.php
index 76a53fdb4..61d531cdf 100644
--- a/lib/TimezoneGuesser/GuessFromCustomizedTimeZone.php
+++ b/lib/TimezoneGuesser/GuessFromCustomizedTimeZone.php
@@ -4,21 +4,19 @@
 
 namespace Sabre\VObject\TimezoneGuesser;
 
-use DateTimeZone;
-use DateTimeImmutable;
 use Sabre\VObject\Component\VTimeZone;
 use Sabre\VObject\Recur\RRuleIterator;
 use Sabre\VObject\TimeZoneUtil;
 
 class GuessFromCustomizedTimeZone implements TimezoneGuesser
 {
-    public function guess(VTimeZone $vtimezone, bool $failIfUncertain = false): ?DateTimeZone
+    public function guess(VTimeZone $vtimezone, ?bool $failIfUncertain = false): ?\DateTimeZone
     {
-        if (null === $vtimezone->TZID || $vtimezone->TZID->getValue() !== 'Customized Time Zone') {
+        if (null === $vtimezone->TZID || 'Customized Time Zone' !== $vtimezone->TZID->getValue()) {
             return null;
         }
 
-        $timezones = DateTimeZone::listIdentifiers();
+        $timezones = \DateTimeZone::listIdentifiers();
         $standard = $vtimezone->STANDARD;
         $daylight = $vtimezone->DAYLIGHT;
         if (!$standard) {
@@ -34,8 +32,8 @@ public function guess(VTimeZone $vtimezone, bool $failIfUncertain = false): ?Dat
         $standardRRule = $standard->RRULE ? $standard->RRULE->getValue() : 'FREQ=DAILY';
         // The guess will not be perfectly matched since we use the timezone data of the current year
         // It might be wrong if the timezone data changed in the past
-        $year = (new DateTimeImmutable('now'))->format('Y');
-        $start = new DateTimeImmutable($year . '-01-01');
+        $year = (new \DateTimeImmutable('now'))->format('Y');
+        $start = new \DateTimeImmutable($year.'-01-01');
         $standardIterator = new RRuleIterator($standardRRule, $start);
         $standardIterator->next();
 
@@ -48,7 +46,7 @@ public function guess(VTimeZone $vtimezone, bool $failIfUncertain = false): ?Dat
         $daylightIterator && $daylightIterator->next();
 
         foreach ($timezones as $timezone) {
-            $tz = new DateTimeZone($timezone);
+            $tz = new \DateTimeZone($timezone);
             // check standard
             $timestamp = $standardIterator->current()->getTimestamp();
             $transitions = $tz->getTransitions($timestamp, $timestamp + 1);
@@ -88,8 +86,8 @@ private function parseOffsetToInteger(string $offset): int
 
         $time = $time * 60;
 
-        if ($offset[0] === "-") {
-            $time = $time *-1;
+        if ('-' === $offset[0]) {
+            $time = $time * -1;
         }
 
         return $time;
diff --git a/lib/TimezoneGuesser/GuessFromLicEntry.php b/lib/TimezoneGuesser/GuessFromLicEntry.php
index b57029919..fbd846e0f 100644
--- a/lib/TimezoneGuesser/GuessFromLicEntry.php
+++ b/lib/TimezoneGuesser/GuessFromLicEntry.php
@@ -4,7 +4,6 @@
 
 namespace Sabre\VObject\TimezoneGuesser;
 
-use DateTimeZone;
 use Sabre\VObject\Component\VTimeZone;
 use Sabre\VObject\TimeZoneUtil;
 
@@ -13,7 +12,7 @@
  */
 class GuessFromLicEntry implements TimezoneGuesser
 {
-    public function guess(VTimeZone $vtimezone, bool $failIfUncertain = false): ?DateTimeZone
+    public function guess(VTimeZone $vtimezone, ?bool $failIfUncertain = false): ?\DateTimeZone
     {
         if (!isset($vtimezone->{'X-LIC-LOCATION'})) {
             return null;
@@ -21,7 +20,7 @@ public function guess(VTimeZone $vtimezone, bool $failIfUncertain = false): ?Dat
 
         $lic = (string) $vtimezone->{'X-LIC-LOCATION'};
 
-        if ($lic === 'Customized Time Zone') {
+        if ('Customized Time Zone' === $lic) {
             return null;
         }
 
diff --git a/lib/TimezoneGuesser/GuessFromMsTzId.php b/lib/TimezoneGuesser/GuessFromMsTzId.php
index b11ce1832..392333cb0 100644
--- a/lib/TimezoneGuesser/GuessFromMsTzId.php
+++ b/lib/TimezoneGuesser/GuessFromMsTzId.php
@@ -4,7 +4,6 @@
 
 namespace Sabre\VObject\TimezoneGuesser;
 
-use DateTimeZone;
 use Sabre\VObject\Component\VTimeZone;
 
 class GuessFromMsTzId implements TimezoneGuesser
@@ -14,12 +13,12 @@ class GuessFromMsTzId implements TimezoneGuesser
      *
      * Source: http://msdn.microsoft.com/en-us/library/aa563018(loband).aspx
      */
-    public static $microsoftExchangeMap = [
+    public static array $microsoftExchangeMap = [
         0 => 'UTC',
         31 => 'Africa/Casablanca',
 
         // Insanely, id #2 is used for both Europe/Lisbon, and Europe/Sarajevo.
-        // I'm not even kidding.. We handle this special case in the
+        // I'm not even kidding. We handle this special case in the
         // getTimeZone method.
         2 => 'Europe/Lisbon',
         1 => 'Europe/London',
@@ -96,7 +95,7 @@ class GuessFromMsTzId implements TimezoneGuesser
         39 => 'Pacific/Kwajalein',
     ];
 
-    public function guess(VTimeZone $vtimezone, bool $throwIfUnsure = false): ?DateTimeZone
+    public function guess(VTimeZone $vtimezone, ?bool $failIfUncertain = false): ?\DateTimeZone
     {
         // Microsoft may add a magic number, which we also have an
         // answer for.
@@ -107,11 +106,11 @@ public function guess(VTimeZone $vtimezone, bool $throwIfUnsure = false): ?DateT
 
         // 2 can mean both Europe/Lisbon and Europe/Sarajevo.
         if (2 === $cdoId && false !== strpos((string) $vtimezone->TZID, 'Sarajevo')) {
-            return new DateTimeZone('Europe/Sarajevo');
+            return new \DateTimeZone('Europe/Sarajevo');
         }
 
         if (isset(self::$microsoftExchangeMap[$cdoId])) {
-            return new DateTimeZone(self::$microsoftExchangeMap[$cdoId]);
+            return new \DateTimeZone(self::$microsoftExchangeMap[$cdoId]);
         }
 
         return null;
diff --git a/lib/TimezoneGuesser/LowercaseTimezoneIdentifier.php b/lib/TimezoneGuesser/LowercaseTimezoneIdentifier.php
index 69fba4424..a6887b941 100644
--- a/lib/TimezoneGuesser/LowercaseTimezoneIdentifier.php
+++ b/lib/TimezoneGuesser/LowercaseTimezoneIdentifier.php
@@ -4,15 +4,13 @@
 
 namespace Sabre\VObject\TimezoneGuesser;
 
-use DateTimeZone;
-
 class LowercaseTimezoneIdentifier implements TimezoneFinder
 {
-    public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
+    public function find(string $tzid, ?bool $failIfUncertain = false): ?\DateTimeZone
     {
-        foreach (DateTimeZone::listIdentifiers() as $timezone) {
+        foreach (\DateTimeZone::listIdentifiers() as $timezone) {
             if (strtolower($tzid) === strtolower($timezone)) {
-                return new DateTimeZone($timezone);
+                return new \DateTimeZone($timezone);
             }
         }
 
diff --git a/lib/TimezoneGuesser/TimezoneFinder.php b/lib/TimezoneGuesser/TimezoneFinder.php
index 5aa880a1c..220459527 100644
--- a/lib/TimezoneGuesser/TimezoneFinder.php
+++ b/lib/TimezoneGuesser/TimezoneFinder.php
@@ -2,9 +2,7 @@
 
 namespace Sabre\VObject\TimezoneGuesser;
 
-use DateTimeZone;
-
 interface TimezoneFinder
 {
-    public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone;
+    public function find(string $tzid, ?bool $failIfUncertain = false): ?\DateTimeZone;
 }
diff --git a/lib/TimezoneGuesser/TimezoneGuesser.php b/lib/TimezoneGuesser/TimezoneGuesser.php
index 5e193bb52..f92eeb210 100644
--- a/lib/TimezoneGuesser/TimezoneGuesser.php
+++ b/lib/TimezoneGuesser/TimezoneGuesser.php
@@ -2,10 +2,9 @@
 
 namespace Sabre\VObject\TimezoneGuesser;
 
-use DateTimeZone;
 use Sabre\VObject\Component\VTimeZone;
 
 interface TimezoneGuesser
 {
-    public function guess(VTimeZone $vtimezone, bool $failIfUncertain = false): ?DateTimeZone;
+    public function guess(VTimeZone $vtimezone, ?bool $failIfUncertain = false): ?\DateTimeZone;
 }
diff --git a/lib/UUIDUtil.php b/lib/UUIDUtil.php
index 066af624c..e8208630c 100644
--- a/lib/UUIDUtil.php
+++ b/lib/UUIDUtil.php
@@ -21,42 +21,36 @@ class UUIDUtil
      * This function is based on a comment by Andrew Moore on php.net
      *
      * @see http://www.php.net/manual/en/function.uniqid.php#94959
-     *
-     * @return string
      */
-    public static function getUUID()
+    public static function getUUID(): string
     {
         return sprintf(
             '%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
 
             // 32 bits for "time_low"
-            mt_rand(0, 0xffff), mt_rand(0, 0xffff),
+            mt_rand(0, 0xFFFF), mt_rand(0, 0xFFFF),
 
             // 16 bits for "time_mid"
-            mt_rand(0, 0xffff),
+            mt_rand(0, 0xFFFF),
 
             // 16 bits for "time_hi_and_version",
             // four most significant bits holds version number 4
-            mt_rand(0, 0x0fff) | 0x4000,
+            mt_rand(0, 0x0FFF) | 0x4000,
 
             // 16 bits, 8 bits for "clk_seq_hi_res",
             // 8 bits for "clk_seq_low",
             // two most significant bits holds zero and one for variant DCE1.1
-            mt_rand(0, 0x3fff) | 0x8000,
+            mt_rand(0, 0x3FFF) | 0x8000,
 
             // 48 bits for "node"
-            mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff)
+            mt_rand(0, 0xFFFF), mt_rand(0, 0xFFFF), mt_rand(0, 0xFFFF)
         );
     }
 
     /**
      * Checks if a string is a valid UUID.
-     *
-     * @param string $uuid
-     *
-     * @return bool
      */
-    public static function validateUUID($uuid)
+    public static function validateUUID(string $uuid): bool
     {
         return 0 !== preg_match(
             '/^[a-f0-9]{8}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{12}$/i',
diff --git a/lib/VCardConverter.php b/lib/VCardConverter.php
index 04932fe67..88d74602c 100644
--- a/lib/VCardConverter.php
+++ b/lib/VCardConverter.php
@@ -2,6 +2,9 @@
 
 namespace Sabre\VObject;
 
+use Sabre\VObject\Property\Binary;
+use Sabre\VObject\Property\Uri;
+
 /**
  * This utility converts vcards from one version to another.
  *
@@ -26,9 +29,9 @@ class VCardConverter
      *
      * If input and output version are identical, a clone is returned.
      *
-     * @param int $targetVersion
+     * @throws InvalidDataException
      */
-    public function convert(Component\VCard $input, $targetVersion)
+    public function convert(Component\VCard $input, int $targetVersion): Component\VCard
     {
         $inputVersion = $input->getDocumentType();
         if ($inputVersion === $targetVersion) {
@@ -61,9 +64,9 @@ public function convert(Component\VCard $input, $targetVersion)
     /**
      * Handles conversion of a single property.
      *
-     * @param int $targetVersion
+     * @throws InvalidDataException
      */
-    protected function convertProperty(Component\VCard $input, Component\VCard $output, Property $property, $targetVersion)
+    protected function convertProperty(Component\VCard $input, Component\VCard $output, Property $property, int $targetVersion): void
     {
         // Skipping these, those are automatically added.
         if (in_array($property->name, ['VERSION', 'PRODID'])) {
@@ -91,14 +94,15 @@ protected function convertProperty(Component\VCard $input, Component\VCard $outp
 
         if (Document::VCARD30 === $targetVersion) {
             if ($property instanceof Property\Uri && in_array($property->name, ['PHOTO', 'LOGO', 'SOUND'])) {
+                /** @var Property\Uri $newProperty */
                 $newProperty = $this->convertUriToBinary($output, $newProperty);
             } elseif ($property instanceof Property\VCard\DateAndOrTime) {
                 // In vCard 4, the birth year may be optional. This is not the
                 // case for vCard 3. Apple has a workaround for this that
                 // allows applications that support Apple's extension still
-                // omit birthyears in vCard 3, but applications that do not
-                // support this, will just use a random birthyear. We're
-                // choosing 1604 for the birthyear, because that's what apple
+                // omit birth years in vCard 3, but applications that do not
+                // support this, will just use a random birth year. We're
+                // choosing 1604 for the birth year, because that's what apple
                 // uses.
                 $parts = DateTimeParser::parseVCardDateTime($property->getValue());
                 if (is_null($parts['year'])) {
@@ -140,6 +144,8 @@ protected function convertProperty(Component\VCard $input, Component\VCard $outp
                         $newProperty = $output->createProperty('X-ADDRESSBOOKSERVER-KIND', 'GROUP');
                         break;
                 }
+            } elseif ('MEMBER' === $property->name) {
+                $newProperty = $output->createProperty('X-ADDRESSBOOKSERVER-MEMBER', $property->getValue());
             }
         } elseif (Document::VCARD40 === $targetVersion) {
             // These properties were removed in vCard 4.0
@@ -148,6 +154,7 @@ protected function convertProperty(Component\VCard $input, Component\VCard $outp
             }
 
             if ($property instanceof Property\Binary) {
+                /** @var Property\Binary $newProperty */
                 $newProperty = $this->convertBinaryToUri($output, $newProperty, $parameters);
             } elseif ($property instanceof Property\VCard\DateAndOrTime && isset($parameters['X-APPLE-OMIT-YEAR'])) {
                 // If a property such as BDAY contained 'X-APPLE-OMIT-YEAR',
@@ -173,6 +180,9 @@ protected function convertProperty(Component\VCard $input, Component\VCard $outp
                         $newProperty = $output->createProperty('KIND', 'GROUP');
                     }
                     break;
+                case 'X-ADDRESSBOOKSERVER-MEMBER':
+                    $newProperty = $output->createProperty('MEMBER', $property->getValue());
+                    break;
                 case 'X-ANNIVERSARY':
                     $newProperty->name = 'ANNIVERSARY';
                     // If we already have an anniversary property with the same
@@ -204,7 +214,7 @@ protected function convertProperty(Component\VCard $input, Component\VCard $outp
                     }
                     $newProperty->name = 'ANNIVERSARY';
                     break;
-                // Apple's per-property label system.
+                    // Apple's per-property label system.
                 case 'X-ABLABEL':
                     if ('_$!<Anniversary>!$_' === $newProperty->getValue()) {
                         // We can safely remove these, as they are converted to
@@ -226,7 +236,7 @@ protected function convertProperty(Component\VCard $input, Component\VCard $outp
 
         // Lastly, we need to see if there's a need for a VALUE parameter.
         //
-        // We can do that by instantiating a empty property with that name, and
+        // We can do that by instantiating an empty property with that name, and
         // seeing if the default valueType is identical to the current one.
         $tempProperty = $output->createProperty($newProperty->name);
         if ($tempProperty->getValueType() !== $newProperty->getValueType()) {
@@ -241,15 +251,15 @@ protected function convertProperty(Component\VCard $input, Component\VCard $outp
      *
      * vCard 4.0 no longer supports BINARY properties.
      *
-     * @param Property\Uri $property the input property
-     * @param $parameters list of parameters that will eventually be added to
-     *                    the new property
+     * @param array $parameters list of parameters that will eventually be added to
+     *                          the new property
      *
-     * @return Property\Uri
+     * @throws InvalidDataException
      */
-    protected function convertBinaryToUri(Component\VCard $output, Property\Binary $newProperty, array &$parameters)
+    protected function convertBinaryToUri(Component\VCard $output, Property\Binary $newProperty, array &$parameters): Uri
     {
         $value = $newProperty->getValue();
+        /** @var Uri $newProperty */
         $newProperty = $output->createProperty(
             $newProperty->name,
             null, // no value
@@ -294,11 +304,11 @@ protected function convertBinaryToUri(Component\VCard $output, Property\Binary $
      * be valid in vCard 3.0 as well, we should convert those to BINARY if
      * possible, to improve compatibility.
      *
-     * @param Property\Uri $property the input property
+     * @return Property\Binary|Property\Uri|null
      *
-     * @return Property\Binary|null
+     * @throws InvalidDataException
      */
-    protected function convertUriToBinary(Component\VCard $output, Property\Uri $newProperty)
+    protected function convertUriToBinary(Component\VCard $output, Property\Uri $newProperty): Property
     {
         $value = $newProperty->getValue();
 
@@ -307,6 +317,7 @@ protected function convertUriToBinary(Component\VCard $output, Property\Uri $new
             return $newProperty;
         }
 
+        /** @var Binary $newProperty */
         $newProperty = $output->createProperty(
             $newProperty->name,
             null, // no value
@@ -342,7 +353,7 @@ protected function convertUriToBinary(Component\VCard $output, Property\Uri $new
     /**
      * Adds parameters to a new property for vCard 4.0.
      */
-    protected function convertParameters40(Property $newProperty, array $parameters)
+    protected function convertParameters40(Property $newProperty, array $parameters): void
     {
         // Adding all parameters.
         foreach ($parameters as $param) {
@@ -363,7 +374,7 @@ protected function convertParameters40(Property $newProperty, array $parameters)
                         }
                     }
                     break;
-                // These no longer exist in vCard 4
+                    // These no longer exist in vCard 4
                 case 'ENCODING':
                 case 'CHARSET':
                     break;
@@ -378,7 +389,7 @@ protected function convertParameters40(Property $newProperty, array $parameters)
     /**
      * Adds parameters to a new property for vCard 3.0.
      */
-    protected function convertParameters30(Property $newProperty, array $parameters)
+    protected function convertParameters30(Property $newProperty, array $parameters): void
     {
         // Adding all parameters.
         foreach ($parameters as $param) {
@@ -396,11 +407,11 @@ protected function convertParameters30(Property $newProperty, array $parameters)
                     }
                     break;
 
-                /*
-                 * Converting PREF=1 to TYPE=PREF.
-                 *
-                 * Any other PREF numbers we'll drop.
-                 */
+                    /*
+                     * Converting PREF=1 to TYPE=PREF.
+                     *
+                     * Any other PREF numbers we'll drop.
+                     */
                 case 'PREF':
                     if ('1' == $param->getValue()) {
                         $newProperty->add('TYPE', 'PREF');
diff --git a/lib/Version.php b/lib/Version.php
index 6b7729caa..fd597c050 100644
--- a/lib/Version.php
+++ b/lib/Version.php
@@ -14,5 +14,5 @@ class Version
     /**
      * Full version number.
      */
-    const VERSION = '4.28.0';
+    public const VERSION = '4.28.0';
 }
diff --git a/lib/Writer.php b/lib/Writer.php
index cbd22022e..504e38a7d 100644
--- a/lib/Writer.php
+++ b/lib/Writer.php
@@ -18,32 +18,24 @@ class Writer
 {
     /**
      * Serializes a vCard or iCalendar object.
-     *
-     * @return string
      */
-    public static function write(Component $component)
+    public static function write(Component $component): string
     {
         return $component->serialize();
     }
 
     /**
      * Serializes a jCal or jCard object.
-     *
-     * @param int $options
-     *
-     * @return string
      */
-    public static function writeJson(Component $component, $options = 0)
+    public static function writeJson(Component $component, int $options = 0): string
     {
         return json_encode($component, $options);
     }
 
     /**
      * Serializes a xCal or xCard object.
-     *
-     * @return string
      */
-    public static function writeXml(Component $component)
+    public static function writeXml(Component $component): string
     {
         $writer = new Xml\Writer();
         $writer->openMemory();
diff --git a/lib/timezonedata/extrazones.php b/lib/timezonedata/extrazones.php
index 711833520..8e477eb99 100644
--- a/lib/timezonedata/extrazones.php
+++ b/lib/timezonedata/extrazones.php
@@ -2,7 +2,7 @@
 
 /**
  * The following list are extra timezones partially extracted from
- * https://unicode-org.github.io/cldr-staging/charts/37/supplemental/zone_tzid.html
+ * https://unicode-org.github.io/cldr-staging/charts/37/supplemental/zone_tzid.html.
  */
 return [
     'Acre' => 'America/Rio_Branco',
diff --git a/lib/timezonedata/lotuszones.php b/lib/timezonedata/lotuszones.php
index 4ba6e3cbe..684a0c972 100644
--- a/lib/timezonedata/lotuszones.php
+++ b/lib/timezonedata/lotuszones.php
@@ -40,7 +40,7 @@
     // 'Mid-Atlantic'           => 'Etc/GMT-2', // conflict with windows timezones.
     'Azores' => 'Atlantic/Azores',
     'Cape Verde' => 'Atlantic/Cape_Verde',
-    'Greenwich' => 'Atlantic/Reykjavik', // No I'm serious.. Greenwich is not GMT.
+    'Greenwich' => 'Atlantic/Reykjavik', // No I'm serious. Greenwich is not GMT.
     'Morocco' => 'Africa/Casablanca',
     'Central Europe' => 'Europe/Prague',
     'Central European' => 'Europe/Sarajevo',
diff --git a/tests/VObject/AttachIssueTest.php b/tests/VObject/AttachIssueTest.php
index fb2b8b037..6f8981a37 100644
--- a/tests/VObject/AttachIssueTest.php
+++ b/tests/VObject/AttachIssueTest.php
@@ -6,7 +6,7 @@
 
 class AttachIssueTest extends TestCase
 {
-    public function testRead()
+    public function testRead(): void
     {
         $event = <<<ICS
 BEGIN:VCALENDAR\r
@@ -17,6 +17,6 @@ public function testRead()
 
 ICS;
         $obj = Reader::read($event);
-        $this->assertEquals($event, $obj->serialize());
+        self::assertEquals($event, $obj->serialize());
     }
 }
diff --git a/tests/VObject/BirthdayCalendarGeneratorTest.php b/tests/VObject/BirthdayCalendarGeneratorTest.php
index d27362837..ac69d1f0b 100644
--- a/tests/VObject/BirthdayCalendarGeneratorTest.php
+++ b/tests/VObject/BirthdayCalendarGeneratorTest.php
@@ -8,7 +8,7 @@ class BirthdayCalendarGeneratorTest extends TestCase
 {
     use PHPUnitAssertions;
 
-    public function testVcardStringWithValidBirthday()
+    public function testVcardStringWithValidBirthday(): void
     {
         $generator = new BirthdayCalendarGenerator();
         $input = <<<VCF
@@ -39,13 +39,13 @@ public function testVcardStringWithValidBirthday()
         $generator->setObjects($input);
         $output = $generator->getResult();
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $output
         );
     }
 
-    public function testArrayOfVcardStringsWithValidBirthdays()
+    public function testArrayOfVcardStringsWithValidBirthdays(): void
     {
         $generator = new BirthdayCalendarGenerator();
         $input = [];
@@ -97,13 +97,13 @@ public function testArrayOfVcardStringsWithValidBirthdays()
         $generator->setObjects($input);
         $output = $generator->getResult();
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $output
         );
     }
 
-    public function testArrayOfVcardStringsWithValidBirthdaysViaConstructor()
+    public function testArrayOfVcardStringsWithValidBirthdaysViaConstructor(): void
     {
         $input = [];
 
@@ -156,13 +156,13 @@ public function testArrayOfVcardStringsWithValidBirthdaysViaConstructor()
         $generator->setObjects($input);
         $output = $generator->getResult();
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $output
         );
     }
 
-    public function testVcardObjectWithValidBirthday()
+    public function testVcardObjectWithValidBirthday(): void
     {
         $generator = new BirthdayCalendarGenerator();
         $input = <<<VCF
@@ -195,13 +195,13 @@ public function testVcardObjectWithValidBirthday()
         $generator->setObjects($input);
         $output = $generator->getResult();
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $output
         );
     }
 
-    public function testArrayOfVcardObjectsWithValidBirthdays()
+    public function testArrayOfVcardObjectsWithValidBirthdays(): void
     {
         $generator = new BirthdayCalendarGenerator();
         $input = [];
@@ -257,13 +257,13 @@ public function testArrayOfVcardObjectsWithValidBirthdays()
         $generator->setObjects($input);
         $output = $generator->getResult();
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $output
         );
     }
 
-    public function testVcardStringWithValidBirthdayWithXAppleOmitYear()
+    public function testVcardStringWithValidBirthdayWithXAppleOmitYear(): void
     {
         $generator = new BirthdayCalendarGenerator();
         $input = <<<VCF
@@ -294,13 +294,13 @@ public function testVcardStringWithValidBirthdayWithXAppleOmitYear()
         $generator->setObjects($input);
         $output = $generator->getResult();
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $output
         );
     }
 
-    public function testVcardStringWithValidBirthdayWithoutYear()
+    public function testVcardStringWithValidBirthdayWithoutYear(): void
     {
         $generator = new BirthdayCalendarGenerator();
         $input = <<<VCF
@@ -331,13 +331,13 @@ public function testVcardStringWithValidBirthdayWithoutYear()
         $generator->setObjects($input);
         $output = $generator->getResult();
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $output
         );
     }
 
-    public function testVcardStringWithInvalidBirthday()
+    public function testVcardStringWithInvalidBirthday(): void
     {
         $generator = new BirthdayCalendarGenerator();
         $input = <<<VCF
@@ -359,13 +359,13 @@ public function testVcardStringWithInvalidBirthday()
         $generator->setObjects($input);
         $output = $generator->getResult();
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $output
         );
     }
 
-    public function testVcardStringWithNoBirthday()
+    public function testVcardStringWithNoBirthday(): void
     {
         $generator = new BirthdayCalendarGenerator();
         $input = <<<VCF
@@ -386,13 +386,13 @@ public function testVcardStringWithNoBirthday()
         $generator->setObjects($input);
         $output = $generator->getResult();
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $output
         );
     }
 
-    public function testVcardStringWithValidBirthdayLocalized()
+    public function testVcardStringWithValidBirthdayLocalized(): void
     {
         $generator = new BirthdayCalendarGenerator();
         $input = <<<VCF
@@ -424,13 +424,13 @@ public function testVcardStringWithValidBirthdayLocalized()
         $generator->setFormat('%1$s\'s Geburtstag');
         $output = $generator->getResult();
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $output
         );
     }
 
-    public function testVcardStringWithEmptyBirthdayProperty()
+    public function testVcardStringWithEmptyBirthdayProperty(): void
     {
         $generator = new BirthdayCalendarGenerator();
         $input = <<<VCF
@@ -452,13 +452,13 @@ public function testVcardStringWithEmptyBirthdayProperty()
         $generator->setObjects($input);
         $output = $generator->getResult();
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $output
         );
     }
 
-    public function testParseException()
+    public function testParseException(): void
     {
         $this->expectException(ParseException::class);
         $generator = new BirthdayCalendarGenerator();
@@ -471,7 +471,7 @@ public function testParseException()
         $generator->setObjects($input);
     }
 
-    public function testInvalidArgumentException()
+    public function testInvalidArgumentException(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $generator = new BirthdayCalendarGenerator();
@@ -488,7 +488,7 @@ public function testInvalidArgumentException()
         $generator->setObjects($input);
     }
 
-    public function testInvalidArgumentExceptionForPartiallyInvalidArray()
+    public function testInvalidArgumentExceptionForPartiallyInvalidArray(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $generator = new BirthdayCalendarGenerator();
@@ -513,7 +513,7 @@ public function testInvalidArgumentExceptionForPartiallyInvalidArray()
         $generator->setObjects($input);
     }
 
-    public function testBrokenVcardWithoutFN()
+    public function testBrokenVcardWithoutFN(): void
     {
         $generator = new BirthdayCalendarGenerator();
         $input = <<<VCF
@@ -534,7 +534,7 @@ public function testBrokenVcardWithoutFN()
         $generator->setObjects($input);
         $output = $generator->getResult();
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $output
         );
diff --git a/tests/VObject/CliTest.php b/tests/VObject/CliTest.php
index a4124b76b..c57d25226 100644
--- a/tests/VObject/CliTest.php
+++ b/tests/VObject/CliTest.php
@@ -11,10 +11,9 @@
  */
 class CliTest extends TestCase
 {
-    /** @var CliMock */
-    private $cli;
+    private CliMock $cli;
 
-    private $sabreTempDir = __DIR__.'/../temp/';
+    private string $sabreTempDir = __DIR__.'/../temp/';
 
     public function setUp(): void
     {
@@ -27,105 +26,105 @@ public function setUp(): void
         $this->cli->stdout = fopen('php://memory', 'r+');
     }
 
-    public function testInvalidArg()
+    public function testInvalidArg(): void
     {
-        $this->assertEquals(
+        self::assertEquals(
             1,
             $this->cli->main(['vobject', '--hi'])
         );
         rewind($this->cli->stderr);
-        $this->assertTrue(strlen(stream_get_contents($this->cli->stderr)) > 100);
+        self::assertTrue(strlen(stream_get_contents($this->cli->stderr)) > 100);
     }
 
-    public function testQuiet()
+    public function testQuiet(): void
     {
-        $this->assertEquals(
+        self::assertEquals(
             1,
             $this->cli->main(['vobject', '-q'])
         );
-        $this->assertTrue($this->cli->quiet);
+        self::assertTrue($this->cli->quiet);
 
         rewind($this->cli->stderr);
-        $this->assertEquals(0, strlen(stream_get_contents($this->cli->stderr)));
+        self::assertEquals(0, strlen(stream_get_contents($this->cli->stderr)));
     }
 
-    public function testHelp()
+    public function testHelp(): void
     {
-        $this->assertEquals(
+        self::assertEquals(
             0,
             $this->cli->main(['vobject', '-h'])
         );
         rewind($this->cli->stderr);
-        $this->assertTrue(strlen(stream_get_contents($this->cli->stderr)) > 100);
+        self::assertTrue(strlen(stream_get_contents($this->cli->stderr)) > 100);
     }
 
-    public function testFormat()
+    public function testFormat(): void
     {
-        $this->assertEquals(
+        self::assertEquals(
             1,
             $this->cli->main(['vobject', '--format=jcard'])
         );
 
         rewind($this->cli->stderr);
-        $this->assertTrue(strlen(stream_get_contents($this->cli->stderr)) > 100);
+        self::assertTrue(strlen(stream_get_contents($this->cli->stderr)) > 100);
 
-        $this->assertEquals('jcard', $this->cli->format);
+        self::assertEquals('jcard', $this->cli->format);
     }
 
-    public function testFormatInvalid()
+    public function testFormatInvalid(): void
     {
-        $this->assertEquals(
+        self::assertEquals(
             1,
             $this->cli->main(['vobject', '--format=foo'])
         );
 
         rewind($this->cli->stderr);
-        $this->assertTrue(strlen(stream_get_contents($this->cli->stderr)) > 100);
+        self::assertTrue(strlen(stream_get_contents($this->cli->stderr)) > 100);
 
-        $this->assertNull($this->cli->format);
+        self::assertNull($this->cli->format);
     }
 
-    public function testInputFormatInvalid()
+    public function testInputFormatInvalid(): void
     {
-        $this->assertEquals(
+        self::assertEquals(
             1,
             $this->cli->main(['vobject', '--inputformat=foo'])
         );
 
         rewind($this->cli->stderr);
-        $this->assertTrue(strlen(stream_get_contents($this->cli->stderr)) > 100);
+        self::assertTrue(strlen(stream_get_contents($this->cli->stderr)) > 100);
 
-        $this->assertNull($this->cli->format);
+        self::assertNull($this->cli->format);
     }
 
-    public function testNoInputFile()
+    public function testNoInputFile(): void
     {
-        $this->assertEquals(
+        self::assertEquals(
             1,
             $this->cli->main(['vobject', 'color'])
         );
 
         rewind($this->cli->stderr);
-        $this->assertTrue(strlen(stream_get_contents($this->cli->stderr)) > 100);
+        self::assertTrue(strlen(stream_get_contents($this->cli->stderr)) > 100);
     }
 
-    public function testTooManyArgs()
+    public function testTooManyArgs(): void
     {
-        $this->assertEquals(
+        self::assertEquals(
             1,
             $this->cli->main(['vobject', 'color', 'a', 'b', 'c'])
         );
     }
 
-    public function testUnknownCommand()
+    public function testUnknownCommand(): void
     {
-        $this->assertEquals(
+        self::assertEquals(
             1,
             $this->cli->main(['vobject', 'foo', '-'])
         );
     }
 
-    public function testConvertJson()
+    public function testConvertJson(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -135,24 +134,24 @@ public function testConvertJson()
 FN:Cowboy Henk
 END:VCARD
 ICS
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
 
-        $this->assertEquals(
+        self::assertEquals(
             0,
             $this->cli->main(['vobject', 'convert', '--format=json', '-'])
         );
 
         rewind($this->cli->stdout);
         $version = Version::VERSION;
-        $this->assertEquals(
+        self::assertEquals(
             '["vcard",[["version",{},"text","4.0"],["prodid",{},"text","-\/\/Sabre\/\/Sabre VObject '.$version.'\/\/EN"],["fn",{},"text","Cowboy Henk"]]]',
             stream_get_contents($this->cli->stdout)
         );
     }
 
-    public function testConvertJCardPretty()
+    public function testConvertJCardPretty(): void
     {
         if (version_compare(PHP_VERSION, '5.4.0') < 0) {
             $this->markTestSkipped('This test required PHP 5.4.0');
@@ -166,11 +165,11 @@ public function testConvertJCardPretty()
 FN:Cowboy Henk
 END:VCARD
 ICS
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
 
-        $this->assertEquals(
+        self::assertEquals(
             0,
             $this->cli->main(['vobject', 'convert', '--format=jcard', '--pretty', '-'])
         );
@@ -187,13 +186,13 @@ public function testConvertJCardPretty()
             "versi
 JCARD;
 
-        $this->assertStringStartsWith(
+        self::assertStringStartsWith(
             $expected,
             stream_get_contents($this->cli->stdout)
         );
     }
 
-    public function testConvertJCalFail()
+    public function testConvertJCalFail(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -203,17 +202,17 @@ public function testConvertJCalFail()
 FN:Cowboy Henk
 END:VCARD
 ICS
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
 
-        $this->assertEquals(
+        self::assertEquals(
             2,
             $this->cli->main(['vobject', 'convert', '--format=jcal', '--inputformat=mimedir', '-'])
         );
     }
 
-    public function testConvertMimeDir()
+    public function testConvertMimeDir(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -248,11 +247,11 @@ public function testConvertMimeDir()
     ]
 ]
 JCARD
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
 
-        $this->assertEquals(
+        self::assertEquals(
             0,
             $this->cli->main(['vobject', 'convert', '--format=mimedir', '--inputformat=json', '--pretty', '-'])
         );
@@ -267,39 +266,39 @@ public function testConvertMimeDir()
 
 VCF;
 
-        $this->assertEquals(
+        self::assertEquals(
             strtr($expected, ["\n" => "\r\n"]),
             stream_get_contents($this->cli->stdout)
         );
     }
 
-    public function testConvertDefaultFormats()
+    public function testConvertDefaultFormats(): void
     {
         $outputFile = $this->sabreTempDir.'bar.json';
 
-        $this->assertEquals(
+        self::assertEquals(
             2,
             $this->cli->main(['vobject', 'convert', 'foo.json', $outputFile])
         );
 
-        $this->assertEquals('json', $this->cli->inputFormat);
-        $this->assertEquals('json', $this->cli->format);
+        self::assertEquals('json', $this->cli->inputFormat);
+        self::assertEquals('json', $this->cli->format);
     }
 
-    public function testConvertDefaultFormats2()
+    public function testConvertDefaultFormats2(): void
     {
         $outputFile = $this->sabreTempDir.'bar.ics';
 
-        $this->assertEquals(
+        self::assertEquals(
             2,
             $this->cli->main(['vobject', 'convert', 'foo.ics', $outputFile])
         );
 
-        $this->assertEquals('mimedir', $this->cli->inputFormat);
-        $this->assertEquals('mimedir', $this->cli->format);
+        self::assertEquals('mimedir', $this->cli->inputFormat);
+        self::assertEquals('mimedir', $this->cli->format);
     }
 
-    public function testVCard3040()
+    public function testVCard3040(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -311,11 +310,11 @@ public function testVCard3040()
 END:VCARD
 
 VCARD
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
 
-        $this->assertEquals(
+        self::assertEquals(
             0,
             $this->cli->main(['vobject', 'convert', '--format=vcard40', '--pretty', '-'])
         );
@@ -332,13 +331,13 @@ public function testVCard3040()
 
 VCF;
 
-        $this->assertEquals(
+        self::assertEquals(
             strtr($expected, ["\n" => "\r\n"]),
             stream_get_contents($this->cli->stdout)
         );
     }
 
-    public function testVCard4030()
+    public function testVCard4030(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -350,11 +349,11 @@ public function testVCard4030()
 END:VCARD
 
 VCARD
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
 
-        $this->assertEquals(
+        self::assertEquals(
             0,
             $this->cli->main(['vobject', 'convert', '--format=vcard30', '--pretty', '-'])
         );
@@ -371,13 +370,13 @@ public function testVCard4030()
 
 VCF;
 
-        $this->assertEquals(
+        self::assertEquals(
             strtr($expected, ["\n" => "\r\n"]),
             stream_get_contents($this->cli->stdout)
         );
     }
 
-    public function testVCard4021()
+    public function testVCard4021(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -389,17 +388,17 @@ public function testVCard4021()
 END:VCARD
 
 VCARD
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
 
-        $this->assertEquals(
+        self::assertEquals(
             2,
             $this->cli->main(['vobject', 'convert', '--format=vcard21', '--pretty', '-'])
         );
     }
 
-    public function testValidate()
+    public function testValidate(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -412,18 +411,18 @@ public function testValidate()
 END:VCARD
 
 VCARD
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
         $result = $this->cli->main(['vobject', 'validate', '-']);
 
-        $this->assertEquals(
+        self::assertEquals(
             0,
             $result
         );
     }
 
-    public function testValidateFail()
+    public function testValidateFail(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -433,17 +432,17 @@ public function testValidateFail()
 END:VCARD
 
 VCARD
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
         // vCard 2.0 is not supported yet, so this returns a failure.
-        $this->assertEquals(
+        self::assertEquals(
             2,
             $this->cli->main(['vobject', 'validate', '-'])
         );
     }
 
-    public function testValidateFail2()
+    public function testValidateFail2(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -453,17 +452,17 @@ public function testValidateFail2()
 END:VCALENDAR
 
 VCARD
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
 
-        $this->assertEquals(
+        self::assertEquals(
             2,
             $this->cli->main(['vobject', 'validate', '-'])
         );
     }
 
-    public function testRepair()
+    public function testRepair(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -473,11 +472,11 @@ public function testRepair()
 END:VCARD
 
 VCARD
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
 
-        $this->assertEquals(
+        self::assertEquals(
             2,
             $this->cli->main(['vobject', 'repair', '-'])
         );
@@ -485,16 +484,10 @@ public function testRepair()
         rewind($this->cli->stdout);
         $regularExpression = "/^BEGIN:VCARD\r\nVERSION:2.1\r\nUID:[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\r\nEND:VCARD\r\n$/";
         $data = stream_get_contents($this->cli->stdout);
-        // ToDo: when we do not need to run phpunit 7 or 8, remove this 'if' block and just use
-        //       the new assertMatchesRegularExpression that exists since phpunit 9.
-        if (method_exists($this, 'assertMatchesRegularExpression')) {
-            $this->assertMatchesRegularExpression($regularExpression, $data);
-        } else {
-            $this->assertRegExp($regularExpression, $data);
-        }
+        self::assertMatchesRegularExpression($regularExpression, $data);
     }
 
-    public function testRepairNothing()
+    public function testRepairNothing(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -510,7 +503,7 @@ public function testRepairNothing()
 END:VCALENDAR
 
 VCARD
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
 
@@ -519,7 +512,7 @@ public function testRepairNothing()
         rewind($this->cli->stderr);
         $error = stream_get_contents($this->cli->stderr);
 
-        $this->assertEquals(
+        self::assertEquals(
             0,
             $result,
             "This should have been error free. stderr output:\n".$error
@@ -532,7 +525,7 @@ public function testRepairNothing()
      *
      * The colorizer is not a critical component, it's mostly a debugging tool.
      */
-    public function testColorCalendar()
+    public function testColorCalendar(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -556,7 +549,7 @@ public function testColorCalendar()
 END:VCALENDAR
 
 VCARD
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
 
@@ -565,7 +558,7 @@ public function testColorCalendar()
         rewind($this->cli->stderr);
         $error = stream_get_contents($this->cli->stderr);
 
-        $this->assertEquals(
+        self::assertEquals(
             0,
             $result,
             "This should have been error free. stderr output:\n".$error
@@ -578,7 +571,7 @@ public function testColorCalendar()
      *
      * The colorizer is not a critical component, it's mostly a debugging tool.
      */
-    public function testColorVCard()
+    public function testColorVCard(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
@@ -597,7 +590,7 @@ public function testColorVCard()
 END:VCARD
 
 VCARD
-    );
+        );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
 
@@ -606,7 +599,7 @@ public function testColorVCard()
         rewind($this->cli->stderr);
         $error = stream_get_contents($this->cli->stderr);
 
-        $this->assertEquals(
+        self::assertEquals(
             0,
             $result,
             "This should have been error free. stderr output:\n".$error
@@ -616,19 +609,32 @@ public function testColorVCard()
 
 class CliMock extends Cli
 {
-    public $quiet = false;
+    public bool $quiet = false;
 
-    public $format;
+    public ?string $format = null;
 
-    public $pretty;
+    public bool $pretty = false;
 
+    /**
+     * stdin.
+     *
+     * @var resource
+     */
     public $stdin;
 
+    /**
+     * output stream.
+     *
+     * @var resource
+     */
     public $stdout;
 
+    /**
+     * stderr.
+     *
+     * @var resource
+     */
     public $stderr;
 
-    public $inputFormat;
-
-    public $outputFormat;
+    public ?string $inputFormat = null;
 }
diff --git a/tests/VObject/Component/AvailableTest.php b/tests/VObject/Component/AvailableTest.php
index bf0a6716f..98202ffcb 100644
--- a/tests/VObject/Component/AvailableTest.php
+++ b/tests/VObject/Component/AvailableTest.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\Component;
 
-use DateTimeImmutable;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Reader;
 
@@ -13,7 +11,7 @@
  */
 class AvailableTest extends TestCase
 {
-    public function testAvailableComponent()
+    public function testAvailableComponent(): void
     {
         $vcal = <<<VCAL
 BEGIN:VCALENDAR
@@ -22,10 +20,10 @@ public function testAvailableComponent()
 END:VCALENDAR
 VCAL;
         $document = Reader::read($vcal);
-        $this->assertInstanceOf(Available::class, $document->AVAILABLE);
+        self::assertInstanceOf(Available::class, $document->AVAILABLE);
     }
 
-    public function testGetEffectiveStartEnd()
+    public function testGetEffectiveStartEnd(): void
     {
         $vcal = <<<VCAL
 BEGIN:VCALENDAR
@@ -37,17 +35,17 @@ public function testGetEffectiveStartEnd()
 VCAL;
 
         $document = Reader::read($vcal);
-        $tz = new DateTimeZone('UTC');
-        $this->assertEquals(
+        $tz = new \DateTimeZone('UTC');
+        self::assertEquals(
             [
-                new DateTimeImmutable('2015-07-17 16:22:00', $tz),
-                new DateTimeImmutable('2015-07-17 17:22:00', $tz),
+                new \DateTimeImmutable('2015-07-17 16:22:00', $tz),
+                new \DateTimeImmutable('2015-07-17 17:22:00', $tz),
             ],
             $document->AVAILABLE->getEffectiveStartEnd()
         );
     }
 
-    public function testGetEffectiveStartEndDuration()
+    public function testGetEffectiveStartEndDuration(): void
     {
         $vcal = <<<VCAL
 BEGIN:VCALENDAR
@@ -59,11 +57,11 @@ public function testGetEffectiveStartEndDuration()
 VCAL;
 
         $document = Reader::read($vcal);
-        $tz = new DateTimeZone('UTC');
-        $this->assertEquals(
+        $tz = new \DateTimeZone('UTC');
+        self::assertEquals(
             [
-                new DateTimeImmutable('2015-07-17 16:22:00', $tz),
-                new DateTimeImmutable('2015-07-17 17:22:00', $tz),
+                new \DateTimeImmutable('2015-07-17 16:22:00', $tz),
+                new \DateTimeImmutable('2015-07-17 17:22:00', $tz),
             ],
             $document->AVAILABLE->getEffectiveStartEnd()
         );
diff --git a/tests/VObject/Component/VAlarmTest.php b/tests/VObject/Component/VAlarmTest.php
index 2823d16da..4694d6363 100644
--- a/tests/VObject/Component/VAlarmTest.php
+++ b/tests/VObject/Component/VAlarmTest.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Component;
 
-use DateTime;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\InvalidDataException;
 use Sabre\VObject\Reader;
@@ -12,12 +11,12 @@ class VAlarmTest extends TestCase
     /**
      * @dataProvider timeRangeTestData
      */
-    public function testInTimeRange(VAlarm $valarm, $start, $end, $outcome)
+    public function testInTimeRange(VAlarm $valarm, \DateTime $start, \DateTime $end, bool $outcome): void
     {
-        $this->assertEquals($outcome, $valarm->isInTimeRange($start, $end));
+        self::assertEquals($outcome, $valarm->isInTimeRange($start, $end));
     }
 
-    public function timeRangeTestData()
+    public function timeRangeTestData(): array
     {
         $tests = [];
 
@@ -29,8 +28,8 @@ public function timeRangeTestData()
             $calendar->createProperty('TRIGGER', '20120312T130000Z', ['VALUE' => 'DATE-TIME'])
         );
 
-        $tests[] = [$valarm1, new DateTime('2012-03-01 01:00:00'), new DateTime('2012-04-01 01:00:00'), true];
-        $tests[] = [$valarm1, new DateTime('2012-03-01 01:00:00'), new DateTime('2012-03-10 01:00:00'), false];
+        $tests[] = [$valarm1, new \DateTime('2012-03-01 01:00:00'), new \DateTime('2012-04-01 01:00:00'), true];
+        $tests[] = [$valarm1, new \DateTime('2012-03-01 01:00:00'), new \DateTime('2012-03-10 01:00:00'), false];
 
         // Relation to start time of event
         $valarm2 = $calendar->createComponent('VALARM');
@@ -42,8 +41,8 @@ public function timeRangeTestData()
         $vevent2->DTSTART = '20120313T130000Z';
         $vevent2->add($valarm2);
 
-        $tests[] = [$valarm2, new DateTime('2012-03-01 01:00:00'), new DateTime('2012-04-01 01:00:00'), true];
-        $tests[] = [$valarm2, new DateTime('2012-03-01 01:00:00'), new DateTime('2012-03-10 01:00:00'), false];
+        $tests[] = [$valarm2, new \DateTime('2012-03-01 01:00:00'), new \DateTime('2012-04-01 01:00:00'), true];
+        $tests[] = [$valarm2, new \DateTime('2012-03-01 01:00:00'), new \DateTime('2012-03-10 01:00:00'), false];
 
         // Relation to end time of event
         $valarm3 = $calendar->createComponent('VALARM');
@@ -54,8 +53,8 @@ public function timeRangeTestData()
         $vevent3->DTEND = '20120401T130000Z';
         $vevent3->add($valarm3);
 
-        $tests[] = [$valarm3, new DateTime('2012-02-25 01:00:00'), new DateTime('2012-03-05 01:00:00'), false];
-        $tests[] = [$valarm3, new DateTime('2012-03-25 01:00:00'), new DateTime('2012-04-05 01:00:00'), true];
+        $tests[] = [$valarm3, new \DateTime('2012-02-25 01:00:00'), new \DateTime('2012-03-05 01:00:00'), false];
+        $tests[] = [$valarm3, new \DateTime('2012-03-25 01:00:00'), new \DateTime('2012-04-05 01:00:00'), true];
 
         // Relation to end time of todo
         $valarm4 = $calendar->createComponent('VALARM');
@@ -68,8 +67,8 @@ public function timeRangeTestData()
         $vtodo4->DUE = '20120401T130000Z';
         $vtodo4->add($valarm4);
 
-        $tests[] = [$valarm4, new DateTime('2012-02-25 01:00:00'), new DateTime('2012-03-05 01:00:00'), false];
-        $tests[] = [$valarm4, new DateTime('2012-03-25 01:00:00'), new DateTime('2012-04-05 01:00:00'), true];
+        $tests[] = [$valarm4, new \DateTime('2012-02-25 01:00:00'), new \DateTime('2012-03-05 01:00:00'), false];
+        $tests[] = [$valarm4, new \DateTime('2012-03-25 01:00:00'), new \DateTime('2012-04-05 01:00:00'), true];
 
         // Relation to start time of event + repeat
         $valarm5 = $calendar->createComponent('VALARM');
@@ -82,7 +81,7 @@ public function timeRangeTestData()
         $vevent5->DTSTART = '20120301T130000Z';
         $vevent5->add($valarm5);
 
-        $tests[] = [$valarm5, new DateTime('2012-03-09 01:00:00'), new DateTime('2012-03-10 01:00:00'), true];
+        $tests[] = [$valarm5, new \DateTime('2012-03-09 01:00:00'), new \DateTime('2012-03-10 01:00:00'), true];
 
         // Relation to start time of event + duration, but no repeat
         $valarm6 = $calendar->createComponent('VALARM');
@@ -94,8 +93,8 @@ public function timeRangeTestData()
         $vevent6->DTSTART = '20120313T130000Z';
         $vevent6->add($valarm6);
 
-        $tests[] = [$valarm6, new DateTime('2012-03-01 01:00:00'), new DateTime('2012-04-01 01:00:00'), true];
-        $tests[] = [$valarm6, new DateTime('2012-03-01 01:00:00'), new DateTime('2012-03-10 01:00:00'), false];
+        $tests[] = [$valarm6, new \DateTime('2012-03-01 01:00:00'), new \DateTime('2012-04-01 01:00:00'), true];
+        $tests[] = [$valarm6, new \DateTime('2012-03-01 01:00:00'), new \DateTime('2012-03-10 01:00:00'), false];
 
         // Relation to end time of event (DURATION instead of DTEND)
         $valarm7 = $calendar->createComponent('VALARM');
@@ -108,8 +107,8 @@ public function timeRangeTestData()
         $vevent7->DURATION = 'P30D';
         $vevent7->add($valarm7);
 
-        $tests[] = [$valarm7, new DateTime('2012-02-25 01:00:00'), new DateTime('2012-03-05 01:00:00'), false];
-        $tests[] = [$valarm7, new DateTime('2012-03-25 01:00:00'), new DateTime('2012-04-05 01:00:00'), true];
+        $tests[] = [$valarm7, new \DateTime('2012-02-25 01:00:00'), new \DateTime('2012-03-05 01:00:00'), false];
+        $tests[] = [$valarm7, new \DateTime('2012-03-25 01:00:00'), new \DateTime('2012-04-05 01:00:00'), true];
 
         // Relation to end time of event (No DTEND or DURATION)
         $valarm7 = $calendar->createComponent('VALARM');
@@ -121,13 +120,13 @@ public function timeRangeTestData()
         $vevent7->DTSTART = '20120301T130000Z';
         $vevent7->add($valarm7);
 
-        $tests[] = [$valarm7, new DateTime('2012-02-25 01:00:00'), new DateTime('2012-03-05 01:00:00'), true];
-        $tests[] = [$valarm7, new DateTime('2012-03-25 01:00:00'), new DateTime('2012-04-05 01:00:00'), false];
+        $tests[] = [$valarm7, new \DateTime('2012-02-25 01:00:00'), new \DateTime('2012-03-05 01:00:00'), true];
+        $tests[] = [$valarm7, new \DateTime('2012-03-25 01:00:00'), new \DateTime('2012-04-05 01:00:00'), false];
 
         return $tests;
     }
 
-    public function testInTimeRangeInvalidComponent()
+    public function testInTimeRangeInvalidComponent(): void
     {
         $this->expectException(InvalidDataException::class);
         $calendar = new VCalendar();
@@ -138,13 +137,13 @@ public function testInTimeRangeInvalidComponent()
         $vjournal = $calendar->createComponent('VJOURNAL');
         $vjournal->add($valarm);
 
-        $valarm->isInTimeRange(new DateTime('2012-02-25 01:00:00'), new DateTime('2012-03-05 01:00:00'));
+        $valarm->isInTimeRange(new \DateTime('2012-02-25 01:00:00'), new \DateTime('2012-03-05 01:00:00'));
     }
 
     /**
      * This bug was found and reported on the mailing list.
      */
-    public function testInTimeRangeBuggy()
+    public function testInTimeRangeBuggy(): void
     {
         $input = <<<BLA
 BEGIN:VCALENDAR
@@ -166,6 +165,6 @@ public function testInTimeRangeBuggy()
 
         $vobj = Reader::read($input);
 
-        $this->assertTrue($vobj->VTODO->VALARM->isInTimeRange(new \DateTime('2012-10-01 00:00:00'), new \DateTime('2012-11-01 00:00:00')));
+        self::assertTrue($vobj->VTODO->VALARM->isInTimeRange(new \DateTime('2012-10-01 00:00:00'), new \DateTime('2012-11-01 00:00:00')));
     }
 }
diff --git a/tests/VObject/Component/VAvailabilityTest.php b/tests/VObject/Component/VAvailabilityTest.php
index edd06b02b..263eeebda 100644
--- a/tests/VObject/Component/VAvailabilityTest.php
+++ b/tests/VObject/Component/VAvailabilityTest.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\Component;
 
-use DateTimeImmutable;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject;
 use Sabre\VObject\Reader;
@@ -14,7 +12,7 @@
  */
 class VAvailabilityTest extends TestCase
 {
-    public function testVAvailabilityComponent()
+    public function testVAvailabilityComponent(): void
     {
         $vcal = <<<VCAL
 BEGIN:VCALENDAR
@@ -24,10 +22,10 @@ public function testVAvailabilityComponent()
 VCAL;
         $document = Reader::read($vcal);
 
-        $this->assertInstanceOf(VAvailability::class, $document->VAVAILABILITY);
+        self::assertInstanceOf(VAvailability::class, $document->VAVAILABILITY);
     }
 
-    public function testGetEffectiveStartEnd()
+    public function testGetEffectiveStartEnd(): void
     {
         $vcal = <<<VCAL
 BEGIN:VCALENDAR
@@ -39,17 +37,17 @@ public function testGetEffectiveStartEnd()
 VCAL;
 
         $document = Reader::read($vcal);
-        $tz = new DateTimeZone('UTC');
-        $this->assertEquals(
+        $tz = new \DateTimeZone('UTC');
+        self::assertEquals(
             [
-                new DateTimeImmutable('2015-07-17 16:22:00', $tz),
-                new DateTimeImmutable('2015-07-17 17:22:00', $tz),
+                new \DateTimeImmutable('2015-07-17 16:22:00', $tz),
+                new \DateTimeImmutable('2015-07-17 17:22:00', $tz),
             ],
             $document->VAVAILABILITY->getEffectiveStartEnd()
         );
     }
 
-    public function testGetEffectiveStartDuration()
+    public function testGetEffectiveStartDuration(): void
     {
         $vcal = <<<VCAL
 BEGIN:VCALENDAR
@@ -61,17 +59,17 @@ public function testGetEffectiveStartDuration()
 VCAL;
 
         $document = Reader::read($vcal);
-        $tz = new DateTimeZone('UTC');
-        $this->assertEquals(
+        $tz = new \DateTimeZone('UTC');
+        self::assertEquals(
             [
-                new DateTimeImmutable('2015-07-17 16:22:00', $tz),
-                new DateTimeImmutable('2015-07-17 17:22:00', $tz),
+                new \DateTimeImmutable('2015-07-17 16:22:00', $tz),
+                new \DateTimeImmutable('2015-07-17 17:22:00', $tz),
             ],
             $document->VAVAILABILITY->getEffectiveStartEnd()
         );
     }
 
-    public function testGetEffectiveStartEndUnbound()
+    public function testGetEffectiveStartEndUnbound(): void
     {
         $vcal = <<<VCAL
 BEGIN:VCALENDAR
@@ -81,7 +79,7 @@ public function testGetEffectiveStartEndUnbound()
 VCAL;
 
         $document = Reader::read($vcal);
-        $this->assertEquals(
+        self::assertEquals(
             [
                 null,
                 null,
@@ -90,7 +88,7 @@ public function testGetEffectiveStartEndUnbound()
         );
     }
 
-    public function testIsInTimeRangeUnbound()
+    public function testIsInTimeRangeUnbound(): void
     {
         $vcal = <<<VCAL
 BEGIN:VCALENDAR
@@ -100,12 +98,12 @@ public function testIsInTimeRangeUnbound()
 VCAL;
 
         $document = Reader::read($vcal);
-        $this->assertTrue(
-            $document->VAVAILABILITY->isInTimeRange(new DateTimeImmutable('2015-07-17'), new DateTimeImmutable('2015-07-18'))
+        self::assertTrue(
+            $document->VAVAILABILITY->isInTimeRange(new \DateTimeImmutable('2015-07-17'), new \DateTimeImmutable('2015-07-18'))
         );
     }
 
-    public function testIsInTimeRangeOutside()
+    public function testIsInTimeRangeOutside(): void
     {
         $vcal = <<<VCAL
 BEGIN:VCALENDAR
@@ -117,16 +115,16 @@ public function testIsInTimeRangeOutside()
 VCAL;
 
         $document = Reader::read($vcal);
-        $this->assertFalse(
-            $document->VAVAILABILITY->isInTimeRange(new DateTimeImmutable('2015-07-17'), new DateTimeImmutable('2015-07-18'))
+        self::assertFalse(
+            $document->VAVAILABILITY->isInTimeRange(new \DateTimeImmutable('2015-07-17'), new \DateTimeImmutable('2015-07-18'))
         );
     }
 
-    public function testRFCxxxSection3Part1AvailabilitypropRequired()
+    public function testRFCxxxSection3Part1AvailabilityPropRequired(): void
     {
         // UID and DTSTAMP are present.
-        $this->assertIsValid(Reader::read(
-<<<VCAL
+        self::assertIsValid(Reader::read(
+            <<<VCAL
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//id
@@ -139,8 +137,8 @@ public function testRFCxxxSection3Part1AvailabilitypropRequired()
         ));
 
         // UID and DTSTAMP are missing.
-        $this->assertIsNotValid(Reader::read(
-<<<VCAL
+        self::assertIsNotValid(Reader::read(
+            <<<VCAL
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//id
@@ -151,8 +149,8 @@ public function testRFCxxxSection3Part1AvailabilitypropRequired()
         ));
 
         // DTSTAMP is missing.
-        $this->assertIsNotValid(Reader::read(
-<<<VCAL
+        self::assertIsNotValid(Reader::read(
+            <<<VCAL
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//id
@@ -164,8 +162,8 @@ public function testRFCxxxSection3Part1AvailabilitypropRequired()
         ));
 
         // UID is missing.
-        $this->assertIsNotValid(Reader::read(
-<<<VCAL
+        self::assertIsNotValid(Reader::read(
+            <<<VCAL
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//id
@@ -177,7 +175,7 @@ public function testRFCxxxSection3Part1AvailabilitypropRequired()
         ));
     }
 
-    public function testRFCxxxSection3Part1AvailabilitypropOptionalOnce()
+    public function testRFCxxxSection3Part1AvailabilityPropOptionalOnce(): void
     {
         $properties = [
             'BUSYTYPE:BUSY',
@@ -194,37 +192,37 @@ public function testRFCxxxSection3Part1AvailabilitypropOptionalOnce()
         ];
 
         // They are all present, only once.
-        $this->assertIsValid(Reader::read($this->template($properties)));
+        self::assertIsValid(Reader::read($this->template($properties)));
 
         // We duplicate each one to see if it fails.
         foreach ($properties as $property) {
-            $this->assertIsNotValid(Reader::read($this->template([
+            self::assertIsNotValid(Reader::read($this->template([
                 $property,
                 $property,
             ])));
         }
     }
 
-    public function testRFCxxxSection3Part1AvailabilitypropDtendDuration()
+    public function testRFCxxxSection3Part1AvailabilityPropDtendDuration(): void
     {
         // Only DTEND.
-        $this->assertIsValid(Reader::read($this->template([
+        self::assertIsValid(Reader::read($this->template([
             'DTEND:21111005T133225Z',
         ])));
 
         // Only DURATION.
-        $this->assertIsValid(Reader::read($this->template([
+        self::assertIsValid(Reader::read($this->template([
             'DURATION:PT1H',
         ])));
 
         // Both (not allowed).
-        $this->assertIsNotValid(Reader::read($this->template([
+        self::assertIsNotValid(Reader::read($this->template([
             'DTEND:21111005T133225Z',
             'DURATION:PT1H',
         ])));
     }
 
-    public function testAvailableSubComponent()
+    public function testAvailableSubComponent(): void
     {
         $vcal = <<<VCAL
 BEGIN:VCALENDAR
@@ -236,14 +234,14 @@ public function testAvailableSubComponent()
 VCAL;
         $document = Reader::read($vcal);
 
-        $this->assertInstanceOf(Available::class, $document->VAVAILABILITY->AVAILABLE);
+        self::assertInstanceOf(Available::class, $document->VAVAILABILITY->AVAILABLE);
     }
 
-    public function testRFCxxxSection3Part1AvailablepropRequired()
+    public function testRFCxxxSection3Part1AvailablePropRequired(): void
     {
         // UID, DTSTAMP and DTSTART are present.
-        $this->assertIsValid(Reader::read(
-<<<VCAL
+        self::assertIsValid(Reader::read(
+            <<<VCAL
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//id
@@ -261,8 +259,8 @@ public function testRFCxxxSection3Part1AvailablepropRequired()
         ));
 
         // UID, DTSTAMP and DTSTART are missing.
-        $this->assertIsNotValid(Reader::read(
-<<<VCAL
+        self::assertIsNotValid(Reader::read(
+            <<<VCAL
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//id
@@ -277,8 +275,8 @@ public function testRFCxxxSection3Part1AvailablepropRequired()
         ));
 
         // UID is missing.
-        $this->assertIsNotValid(Reader::read(
-<<<VCAL
+        self::assertIsNotValid(Reader::read(
+            <<<VCAL
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//id
@@ -295,8 +293,8 @@ public function testRFCxxxSection3Part1AvailablepropRequired()
         ));
 
         // DTSTAMP is missing.
-        $this->assertIsNotValid(Reader::read(
-<<<VCAL
+        self::assertIsNotValid(Reader::read(
+            <<<VCAL
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//id
@@ -313,8 +311,8 @@ public function testRFCxxxSection3Part1AvailablepropRequired()
         ));
 
         // DTSTART is missing.
-        $this->assertIsNotValid(Reader::read(
-<<<VCAL
+        self::assertIsNotValid(Reader::read(
+            <<<VCAL
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//id
@@ -331,26 +329,26 @@ public function testRFCxxxSection3Part1AvailablepropRequired()
         ));
     }
 
-    public function testRFCxxxSection3Part1AvailableDtendDuration()
+    public function testRFCxxxSection3Part1AvailableDtendDuration(): void
     {
         // Only DTEND.
-        $this->assertIsValid(Reader::read($this->templateAvailable([
+        self::assertIsValid(Reader::read($this->templateAvailable([
             'DTEND:21111005T133225Z',
         ])));
 
         // Only DURATION.
-        $this->assertIsValid(Reader::read($this->templateAvailable([
+        self::assertIsValid(Reader::read($this->templateAvailable([
             'DURATION:PT1H',
         ])));
 
         // Both (not allowed).
-        $this->assertIsNotValid(Reader::read($this->templateAvailable([
+        self::assertIsNotValid(Reader::read($this->templateAvailable([
             'DTEND:21111005T133225Z',
             'DURATION:PT1H',
         ])));
     }
 
-    public function testRFCxxxSection3Part1AvailableOptionalOnce()
+    public function testRFCxxxSection3Part1AvailableOptionalOnce(): void
     {
         $properties = [
             'CREATED:20111005T135125Z',
@@ -362,20 +360,20 @@ public function testRFCxxxSection3Part1AvailableOptionalOnce()
         ];
 
         // They are all present, only once.
-        $this->assertIsValid(Reader::read($this->templateAvailable($properties)));
+        self::assertIsValid(Reader::read($this->templateAvailable($properties)));
 
         // We duplicate each one to see if it fails.
         foreach ($properties as $property) {
-            $this->assertIsNotValid(Reader::read($this->templateAvailable([
+            self::assertIsNotValid(Reader::read($this->templateAvailable([
                 $property,
                 $property,
             ])));
         }
     }
 
-    public function testRFCxxxSection3Part2()
+    public function testRFCxxxSection3Part2(): void
     {
-        $this->assertEquals(
+        self::assertEquals(
             'BUSY',
             Reader::read($this->templateAvailable([
                 'BUSYTYPE:BUSY',
@@ -386,7 +384,7 @@ public function testRFCxxxSection3Part2()
                 ->getValue()
         );
 
-        $this->assertEquals(
+        self::assertEquals(
             'BUSY-UNAVAILABLE',
             Reader::read($this->templateAvailable([
                 'BUSYTYPE:BUSY-UNAVAILABLE',
@@ -397,7 +395,7 @@ public function testRFCxxxSection3Part2()
                 ->getValue()
         );
 
-        $this->assertEquals(
+        self::assertEquals(
             'BUSY-TENTATIVE',
             Reader::read($this->templateAvailable([
                 'BUSYTYPE:BUSY-TENTATIVE',
@@ -409,19 +407,19 @@ public function testRFCxxxSection3Part2()
         );
     }
 
-    protected function assertIsValid(VObject\Document $document)
+    protected function assertIsValid(VObject\Document $document): void
     {
         $validationResult = $document->validate();
         if ($validationResult) {
             $messages = array_map(function ($item) { return $item['message']; }, $validationResult);
             $this->fail('Failed to assert that the supplied document is a valid document. Validation messages: '.implode(', ', $messages));
         }
-        $this->assertEmpty($document->validate());
+        self::assertEmpty($document->validate());
     }
 
-    protected function assertIsNotValid(VObject\Document $document)
+    protected function assertIsNotValid(VObject\Document $document): void
     {
-        $this->assertNotEmpty($document->validate());
+        self::assertNotEmpty($document->validate());
     }
 
     protected function template(array $properties)
@@ -438,7 +436,7 @@ protected function template(array $properties)
 END:VAVAILABILITY
 END:VCALENDAR
 VCAL
-,
+            ,
             $properties
         );
     }
@@ -462,7 +460,7 @@ protected function templateAvailable(array $properties)
 END:VAVAILABILITY
 END:VCALENDAR
 VCAL
-,
+            ,
             $properties
         );
     }
diff --git a/tests/VObject/Component/VCalendarTest.php b/tests/VObject/Component/VCalendarTest.php
index d34e12d2b..1893a9ac7 100644
--- a/tests/VObject/Component/VCalendarTest.php
+++ b/tests/VObject/Component/VCalendarTest.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Component;
 
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject;
 use Sabre\VObject\InvalidDataException;
@@ -14,11 +13,11 @@ class VCalendarTest extends TestCase
     /**
      * @dataProvider expandData
      */
-    public function testExpand($input, $output, $timeZone = 'UTC', $start = '2011-12-01', $end = '2011-12-31')
+    public function testExpand(string $input, string $output, string $timeZone = 'UTC', string $start = '2011-12-01', string $end = '2011-12-31'): void
     {
         $vcal = VObject\Reader::read($input);
 
-        $timeZone = new DateTimeZone($timeZone);
+        $timeZone = new \DateTimeZone($timeZone);
 
         $vcal = $vcal->expand(
             new \DateTime($start),
@@ -29,10 +28,10 @@ public function testExpand($input, $output, $timeZone = 'UTC', $start = '2011-12
         // This will normalize the output
         $output = VObject\Reader::read($output)->serialize();
 
-        $this->assertVObjectEqualsVObject($output, $vcal->serialize());
+        self::assertVObjectEqualsVObject($output, $vcal->serialize());
     }
 
-    public function expandData()
+    public function expandData(): array
     {
         $tests = [];
 
@@ -331,7 +330,7 @@ public function expandData()
         return $tests;
     }
 
-    public function testBrokenEventExpand()
+    public function testBrokenEventExpand(): void
     {
         $this->expectException(InvalidDataException::class);
         $input = 'BEGIN:VCALENDAR
@@ -357,7 +356,7 @@ public function testBrokenEventExpand()
      *
      * @medium
      */
-    public function testEventExpandYearly()
+    public function testEventExpandYearly(): void
     {
         $input = 'BEGIN:VCALENDAR
 BEGIN:VEVENT
@@ -374,17 +373,17 @@ public function testEventExpandYearly()
             new \DateTime('2023-01-01')
         );
 
-        $this->assertCount(7, $events->VEVENT);
+        self::assertCount(7, $events->VEVENT);
     }
 
-    public function testGetDocumentType()
+    public function testGetDocumentType(): void
     {
         $vcard = new VCalendar();
         $vcard->VERSION = '2.0';
-        $this->assertEquals(VCalendar::ICALENDAR20, $vcard->getDocumentType());
+        self::assertEquals(VCalendar::ICALENDAR20, $vcard->getDocumentType());
     }
 
-    public function testValidateCorrect()
+    public function testValidateCorrect(): void
     {
         $input = 'BEGIN:VCALENDAR
 CALSCALE:GREGORIAN
@@ -399,10 +398,10 @@ public function testValidateCorrect()
 ';
 
         $vcal = VObject\Reader::read($input);
-        $this->assertEquals([], $vcal->validate(), 'Got an error');
+        self::assertEquals([], $vcal->validate(), 'Got an error');
     }
 
-    public function testValidateNoVersion()
+    public function testValidateNoVersion(): void
     {
         $input = 'BEGIN:VCALENDAR
 CALSCALE:GREGORIAN
@@ -416,10 +415,10 @@ public function testValidateNoVersion()
 ';
 
         $vcal = VObject\Reader::read($input);
-        $this->assertEquals(1, count($vcal->validate()));
+        self::assertCount(1, $vcal->validate());
     }
 
-    public function testValidateWrongVersion()
+    public function testValidateWrongVersion(): void
     {
         $input = 'BEGIN:VCALENDAR
 CALSCALE:GREGORIAN
@@ -434,10 +433,10 @@ public function testValidateWrongVersion()
 ';
 
         $vcal = VObject\Reader::read($input);
-        $this->assertEquals(1, count($vcal->validate()));
+        self::assertCount(1, $vcal->validate());
     }
 
-    public function testValidateNoProdId()
+    public function testValidateNoProdId(): void
     {
         $input = 'BEGIN:VCALENDAR
 CALSCALE:GREGORIAN
@@ -451,10 +450,10 @@ public function testValidateNoProdId()
 ';
 
         $vcal = VObject\Reader::read($input);
-        $this->assertEquals(1, count($vcal->validate()));
+        self::assertCount(1, $vcal->validate());
     }
 
-    public function testValidateDoubleCalScale()
+    public function testValidateDoubleCalScale(): void
     {
         $input = 'BEGIN:VCALENDAR
 VERSION:2.0
@@ -470,10 +469,10 @@ public function testValidateDoubleCalScale()
 ';
 
         $vcal = VObject\Reader::read($input);
-        $this->assertEquals(1, count($vcal->validate()));
+        self::assertCount(1, $vcal->validate());
     }
 
-    public function testValidateDoubleMethod()
+    public function testValidateDoubleMethod(): void
     {
         $input = 'BEGIN:VCALENDAR
 VERSION:2.0
@@ -489,10 +488,10 @@ public function testValidateDoubleMethod()
 ';
 
         $vcal = VObject\Reader::read($input);
-        $this->assertEquals(1, count($vcal->validate()));
+        self::assertCount(1, $vcal->validate());
     }
 
-    public function testValidateTwoMasterEvents()
+    public function testValidateTwoMasterEvents(): void
     {
         $input = 'BEGIN:VCALENDAR
 VERSION:2.0
@@ -512,10 +511,10 @@ public function testValidateTwoMasterEvents()
 ';
 
         $vcal = VObject\Reader::read($input);
-        $this->assertEquals(1, count($vcal->validate()));
+        self::assertCount(1, $vcal->validate());
     }
 
-    public function testValidateOneMasterEvent()
+    public function testValidateOneMasterEvent(): void
     {
         $input = 'BEGIN:VCALENDAR
 VERSION:2.0
@@ -536,10 +535,10 @@ public function testValidateOneMasterEvent()
 ';
 
         $vcal = VObject\Reader::read($input);
-        $this->assertEquals(0, count($vcal->validate()));
+        self::assertCount(0, $vcal->validate());
     }
 
-    public function testGetBaseComponent()
+    public function testGetBaseComponent(): void
     {
         $input = 'BEGIN:VCALENDAR
 VERSION:2.0
@@ -563,10 +562,10 @@ public function testGetBaseComponent()
         $vcal = VObject\Reader::read($input);
 
         $result = $vcal->getBaseComponent();
-        $this->assertEquals('test', $result->SUMMARY->getValue());
+        self::assertEquals('test', $result->SUMMARY->getValue());
     }
 
-    public function testGetBaseComponentNoResult()
+    public function testGetBaseComponentNoResult(): void
     {
         $input = 'BEGIN:VCALENDAR
 VERSION:2.0
@@ -591,10 +590,10 @@ public function testGetBaseComponentNoResult()
         $vcal = VObject\Reader::read($input);
 
         $result = $vcal->getBaseComponent();
-        $this->assertNull($result);
+        self::assertNull($result);
     }
 
-    public function testGetBaseComponentWithFilter()
+    public function testGetBaseComponentWithFilter(): void
     {
         $input = 'BEGIN:VCALENDAR
 VERSION:2.0
@@ -618,10 +617,10 @@ public function testGetBaseComponentWithFilter()
         $vcal = VObject\Reader::read($input);
 
         $result = $vcal->getBaseComponent('VEVENT');
-        $this->assertEquals('test', $result->SUMMARY->getValue());
+        self::assertEquals('test', $result->SUMMARY->getValue());
     }
 
-    public function testGetBaseComponentWithFilterNoResult()
+    public function testGetBaseComponentWithFilterNoResult(): void
     {
         $input = 'BEGIN:VCALENDAR
 VERSION:2.0
@@ -638,10 +637,10 @@ public function testGetBaseComponentWithFilterNoResult()
         $vcal = VObject\Reader::read($input);
 
         $result = $vcal->getBaseComponent('VEVENT');
-        $this->assertNull($result);
+        self::assertNull($result);
     }
 
-    public function testNoComponents()
+    public function testNoComponents(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -650,15 +649,15 @@ public function testNoComponents()
 END:VCALENDAR
 ICS;
 
-        $this->assertValidate(
+        self::assertValidate(
             $input,
             0,
             3,
-           'An iCalendar object must have at least 1 component.'
+            'An iCalendar object must have at least 1 component.'
         );
     }
 
-    public function testCalDAVNoComponents()
+    public function testCalDAVNoComponents(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -670,15 +669,15 @@ public function testCalDAVNoComponents()
 END:VCALENDAR
 ICS;
 
-        $this->assertValidate(
+        self::assertValidate(
             $input,
             VCalendar::PROFILE_CALDAV,
             3,
-           'A calendar object on a CalDAV server must have at least 1 component (VTODO, VEVENT, VJOURNAL).'
+            'A calendar object on a CalDAV server must have at least 1 component (VTODO, VEVENT, VJOURNAL).'
         );
     }
 
-    public function testCalDAVMultiUID()
+    public function testCalDAVMultiUID(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -697,15 +696,15 @@ public function testCalDAVMultiUID()
 END:VCALENDAR
 ICS;
 
-        $this->assertValidate(
+        self::assertValidate(
             $input,
             VCalendar::PROFILE_CALDAV,
             3,
-           'A calendar object on a CalDAV server may only have components with the same UID.'
+            'A calendar object on a CalDAV server may only have components with the same UID.'
         );
     }
 
-    public function testCalDAVMultiComponent()
+    public function testCalDAVMultiComponent(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -725,15 +724,15 @@ public function testCalDAVMultiComponent()
 END:VCALENDAR
 ICS;
 
-        $this->assertValidate(
+        self::assertValidate(
             $input,
             VCalendar::PROFILE_CALDAV,
             3,
-           'A calendar object on a CalDAV server may only have 1 type of component (VEVENT, VTODO or VJOURNAL).'
+            'A calendar object on a CalDAV server may only have 1 type of component (VEVENT, VTODO or VJOURNAL).'
         );
     }
 
-    public function testCalDAVMETHOD()
+    public function testCalDAVMETHOD(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -749,23 +748,23 @@ public function testCalDAVMETHOD()
 END:VCALENDAR
 ICS;
 
-        $this->assertValidate(
+        self::assertValidate(
             $input,
             VCalendar::PROFILE_CALDAV,
             3,
-           'A calendar object on a CalDAV server MUST NOT have a METHOD property.'
+            'A calendar object on a CalDAV server MUST NOT have a METHOD property.'
         );
     }
 
-    public function assertValidate($ics, $options, $expectedLevel, $expectedMessage = null)
+    public function assertValidate($ics, $options, $expectedLevel, string $expectedMessage = null): void
     {
         $vcal = VObject\Reader::read($ics);
         $result = $vcal->validate($options);
 
-        $this->assertValidateResult($result, $expectedLevel, $expectedMessage);
+        self::assertValidateResult($result, $expectedLevel, $expectedMessage);
     }
 
-    public function assertValidateResult($input, $expectedLevel, $expectedMessage = null)
+    public function assertValidateResult($input, $expectedLevel, string $expectedMessage = null): void
     {
         $messages = [];
         foreach ($input as $warning) {
@@ -773,12 +772,12 @@ public function assertValidateResult($input, $expectedLevel, $expectedMessage =
         }
 
         if (0 === $expectedLevel) {
-            $this->assertEquals(0, count($input), 'No validation messages were expected. We got: '.implode(', ', $messages));
+            self::assertCount(0, $input, 'No validation messages were expected. We got: '.implode(', ', $messages));
         } else {
-            $this->assertEquals(1, count($input), 'We expected exactly 1 validation message, We got: '.implode(', ', $messages));
+            self::assertCount(1, $input, 'We expected exactly 1 validation message, We got: '.implode(', ', $messages));
 
-            $this->assertEquals($expectedMessage, $input[0]['message']);
-            $this->assertEquals($expectedLevel, $input[0]['level']);
+            self::assertEquals($expectedMessage, $input[0]['message']);
+            self::assertEquals($expectedLevel, $input[0]['level']);
         }
     }
 }
diff --git a/tests/VObject/Component/VCardTest.php b/tests/VObject/Component/VCardTest.php
index d8e6110b6..b71b30856 100644
--- a/tests/VObject/Component/VCardTest.php
+++ b/tests/VObject/Component/VCardTest.php
@@ -10,7 +10,7 @@ class VCardTest extends TestCase
     /**
      * @dataProvider validateData
      */
-    public function testValidate($input, $expectedWarnings, $expectedRepairedOutput)
+    public function testValidate(string $input, array $expectedWarnings, string $expectedRepairedOutput): void
     {
         $vcard = VObject\Reader::read($input);
 
@@ -21,17 +21,17 @@ public function testValidate($input, $expectedWarnings, $expectedRepairedOutput)
             $warnMsg[] = $warning['message'];
         }
 
-        $this->assertEquals($expectedWarnings, $warnMsg);
+        self::assertEquals($expectedWarnings, $warnMsg);
 
         $vcard->validate(VObject\Component::REPAIR);
 
-        $this->assertEquals(
+        self::assertEquals(
             $expectedRepairedOutput,
             $vcard->serialize()
         );
     }
 
-    public function validateData()
+    public function validateData(): array
     {
         $tests = [];
 
@@ -92,6 +92,14 @@ public function validateData()
             ],
             "BEGIN:VCARD\r\nVERSION:4.0\r\nUID:foo\r\nORG:Acme Co.\r\nFN:Acme Co.\r\nEND:VCARD\r\n",
         ];
+        // No FN, NICKNAME fallback
+        $tests[] = [
+            "BEGIN:VCARD\r\nVERSION:4.0\r\nUID:foo\r\nNICKNAME:JohnDoe\r\nEND:VCARD\r\n",
+            [
+                'The FN property must appear in the VCARD component exactly 1 time',
+            ],
+            "BEGIN:VCARD\r\nVERSION:4.0\r\nUID:foo\r\nNICKNAME:JohnDoe\r\nFN:JohnDoe\r\nEND:VCARD\r\n",
+        ];
         // No FN, EMAIL fallback
         $tests[] = [
             "BEGIN:VCARD\r\nVERSION:4.0\r\nUID:foo\r\nEMAIL:1@example.org\r\nEND:VCARD\r\n",
@@ -104,25 +112,25 @@ public function validateData()
         return $tests;
     }
 
-    public function testGetDocumentType()
+    public function testGetDocumentType(): void
     {
         $vcard = new VCard([], false);
         $vcard->VERSION = '2.1';
-        $this->assertEquals(VCard::VCARD21, $vcard->getDocumentType());
+        self::assertEquals(VCard::VCARD21, $vcard->getDocumentType());
 
         $vcard = new VCard([], false);
         $vcard->VERSION = '3.0';
-        $this->assertEquals(VCard::VCARD30, $vcard->getDocumentType());
+        self::assertEquals(VCard::VCARD30, $vcard->getDocumentType());
 
         $vcard = new VCard([], false);
         $vcard->VERSION = '4.0';
-        $this->assertEquals(VCard::VCARD40, $vcard->getDocumentType());
+        self::assertEquals(VCard::VCARD40, $vcard->getDocumentType());
 
         $vcard = new VCard([], false);
-        $this->assertEquals(VCard::UNKNOWN, $vcard->getDocumentType());
+        self::assertEquals(VCard::UNKNOWN, $vcard->getDocumentType());
     }
 
-    public function testGetByType()
+    public function testGetByType(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -133,13 +141,13 @@ public function testGetByType()
 VCF;
 
         $vcard = VObject\Reader::read($vcard);
-        $this->assertEquals('1@example.org', $vcard->getByType('EMAIL', 'home')->getValue());
-        $this->assertEquals('2@example.org', $vcard->getByType('EMAIL', 'work')->getValue());
-        $this->assertNull($vcard->getByType('EMAIL', 'non-existent'));
-        $this->assertNull($vcard->getByType('ADR', 'non-existent'));
+        self::assertEquals('1@example.org', $vcard->getByType('EMAIL', 'home')->getValue());
+        self::assertEquals('2@example.org', $vcard->getByType('EMAIL', 'work')->getValue());
+        self::assertNull($vcard->getByType('EMAIL', 'non-existent'));
+        self::assertNull($vcard->getByType('ADR', 'non-existent'));
     }
 
-    public function testPreferredNoPref()
+    public function testPreferredNoPref(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -150,10 +158,10 @@ public function testPreferredNoPref()
 VCF;
 
         $vcard = VObject\Reader::read($vcard);
-        $this->assertEquals('1@example.org', $vcard->preferred('EMAIL')->getValue());
+        self::assertEquals('1@example.org', $vcard->preferred('EMAIL')->getValue());
     }
 
-    public function testPreferredWithPref()
+    public function testPreferredWithPref(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -164,10 +172,10 @@ public function testPreferredWithPref()
 VCF;
 
         $vcard = VObject\Reader::read($vcard);
-        $this->assertEquals('2@example.org', $vcard->preferred('EMAIL')->getValue());
+        self::assertEquals('2@example.org', $vcard->preferred('EMAIL')->getValue());
     }
 
-    public function testPreferredWith40Pref()
+    public function testPreferredWith40Pref(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -179,10 +187,10 @@ public function testPreferredWith40Pref()
 VCF;
 
         $vcard = VObject\Reader::read($vcard);
-        $this->assertEquals('3@example.org', $vcard->preferred('EMAIL')->getValue());
+        self::assertEquals('3@example.org', $vcard->preferred('EMAIL')->getValue());
     }
 
-    public function testPreferredNotFound()
+    public function testPreferredNotFound(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -191,10 +199,10 @@ public function testPreferredNotFound()
 VCF;
 
         $vcard = VObject\Reader::read($vcard);
-        $this->assertNull($vcard->preferred('EMAIL'));
+        self::assertNull($vcard->preferred('EMAIL'));
     }
 
-    public function testNoUIDCardDAV()
+    public function testNoUIDCardDAV(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -202,7 +210,7 @@ public function testNoUIDCardDAV()
 FN:John Doe
 END:VCARD
 VCF;
-        $this->assertValidate(
+        self::assertValidate(
             $vcard,
             VCard::PROFILE_CARDDAV,
             3,
@@ -210,7 +218,7 @@ public function testNoUIDCardDAV()
         );
     }
 
-    public function testNoUIDNoCardDAV()
+    public function testNoUIDNoCardDAV(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -218,7 +226,7 @@ public function testNoUIDNoCardDAV()
 FN:John Doe
 END:VCARD
 VCF;
-        $this->assertValidate(
+        self::assertValidate(
             $vcard,
             0,
             2,
@@ -226,7 +234,7 @@ public function testNoUIDNoCardDAV()
         );
     }
 
-    public function testNoUIDNoCardDAVRepair()
+    public function testNoUIDNoCardDAVRepair(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -234,7 +242,7 @@ public function testNoUIDNoCardDAVRepair()
 FN:John Doe
 END:VCARD
 VCF;
-        $this->assertValidate(
+        self::assertValidate(
             $vcard,
             VCard::REPAIR,
             1,
@@ -242,7 +250,7 @@ public function testNoUIDNoCardDAVRepair()
         );
     }
 
-    public function testVCard21CardDAV()
+    public function testVCard21CardDAV(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -251,7 +259,7 @@ public function testVCard21CardDAV()
 UID:foo
 END:VCARD
 VCF;
-        $this->assertValidate(
+        self::assertValidate(
             $vcard,
             VCard::PROFILE_CARDDAV,
             3,
@@ -259,7 +267,7 @@ public function testVCard21CardDAV()
         );
     }
 
-    public function testVCard21NoCardDAV()
+    public function testVCard21NoCardDAV(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -268,22 +276,22 @@ public function testVCard21NoCardDAV()
 UID:foo
 END:VCARD
 VCF;
-        $this->assertValidate(
+        self::assertValidate(
             $vcard,
             0,
             0
         );
     }
 
-    public function assertValidate($vcf, $options, $expectedLevel, $expectedMessage = null)
+    public function assertValidate($vcf, $options, int $expectedLevel, string $expectedMessage = null): void
     {
         $vcal = VObject\Reader::read($vcf);
         $result = $vcal->validate($options);
 
-        $this->assertValidateResult($result, $expectedLevel, $expectedMessage);
+        self::assertValidateResult($result, $expectedLevel, $expectedMessage);
     }
 
-    public function assertValidateResult($input, $expectedLevel, $expectedMessage = null)
+    public function assertValidateResult($input, int $expectedLevel, string $expectedMessage = null): void
     {
         $messages = [];
         foreach ($input as $warning) {
@@ -291,12 +299,12 @@ public function assertValidateResult($input, $expectedLevel, $expectedMessage =
         }
 
         if (0 === $expectedLevel) {
-            $this->assertEquals(0, count($input), 'No validation messages were expected. We got: '.implode(', ', $messages));
+            self::assertCount(0, $input, 'No validation messages were expected. We got: '.implode(', ', $messages));
         } else {
-            $this->assertEquals(1, count($input), 'We expected exactly 1 validation message, We got: '.implode(', ', $messages));
+            self::assertCount(1, $input, 'We expected exactly 1 validation message, We got: '.implode(', ', $messages));
 
-            $this->assertEquals($expectedMessage, $input[0]['message']);
-            $this->assertEquals($expectedLevel, $input[0]['level']);
+            self::assertEquals($expectedMessage, $input[0]['message']);
+            self::assertEquals($expectedLevel, $input[0]['level']);
         }
     }
 }
diff --git a/tests/VObject/Component/VEventTest.php b/tests/VObject/Component/VEventTest.php
index 635ae5acd..50fa626cc 100644
--- a/tests/VObject/Component/VEventTest.php
+++ b/tests/VObject/Component/VEventTest.php
@@ -9,12 +9,12 @@ class VEventTest extends TestCase
     /**
      * @dataProvider timeRangeTestData
      */
-    public function testInTimeRange(VEvent $vevent, $start, $end, $outcome)
+    public function testInTimeRange(VEvent $vevent, \DateTime $start, \DateTime $end, bool $outcome): void
     {
-        $this->assertEquals($outcome, $vevent->isInTimeRange($start, $end));
+        self::assertEquals($outcome, $vevent->isInTimeRange($start, $end));
     }
 
-    public function timeRangeTestData()
+    public function timeRangeTestData(): array
     {
         $tests = [];
 
@@ -42,9 +42,9 @@ public function timeRangeTestData()
         $tests[] = [$vevent4, new \DateTime('2011-01-01'), new \DateTime('2011-11-01'), false];
         // Event with no end date should be treated as lasting the entire day.
         $tests[] = [$vevent4, new \DateTime('2011-12-25 16:00:00'), new \DateTime('2011-12-25 17:00:00'), true];
-        // DTEND is non inclusive so all day events should not be returned on the next day.
+        // DTEND is non-inclusive so all day events should not be returned on the next day.
         $tests[] = [$vevent4, new \DateTime('2011-12-26 00:00:00'), new \DateTime('2011-12-26 17:00:00'), false];
-        // The timezone of timerange in question also needs to be considered.
+        // The timezone of time range in question also needs to be considered.
         $tests[] = [$vevent4, new \DateTime('2011-12-26 00:00:00', new \DateTimeZone('Europe/Berlin')), new \DateTime('2011-12-26 17:00:00', new \DateTimeZone('Europe/Berlin')), false];
 
         $vevent5 = clone $vevent;
@@ -70,7 +70,7 @@ public function timeRangeTestData()
         $vevent7->DTSTART['VALUE'] = 'DATE';
         $vevent7->RRULE = 'FREQ=MONTHLY';
         $tests[] = [$vevent7, new \DateTime('2012-02-01 15:00:00'), new \DateTime('2012-02-02'), true];
-        // The timezone of timerange in question should also be considered.
+        // The timezone of time range in question should also be considered.
         $tests[] = [$vevent7, new \DateTime('2012-02-02 00:00:00', new \DateTimeZone('Europe/Berlin')), new \DateTime('2012-02-03 00:00:00', new \DateTimeZone('Europe/Berlin')), false];
 
         // Added this test to check recurring events that have no instances.
diff --git a/tests/VObject/Component/VFreeBusyTest.php b/tests/VObject/Component/VFreeBusyTest.php
index 2aa4351ca..f3a521f95 100644
--- a/tests/VObject/Component/VFreeBusyTest.php
+++ b/tests/VObject/Component/VFreeBusyTest.php
@@ -8,7 +8,7 @@
 
 class VFreeBusyTest extends TestCase
 {
-    public function testIsFree()
+    public function testIsFree(): void
     {
         $input = <<<BLA
 BEGIN:VCALENDAR
@@ -28,17 +28,17 @@ public function testIsFree()
 
         $tz = new \DateTimeZone('UTC');
 
-        $this->assertFalse($vfb->isFree(new \DateTime('2012-09-12 01:15:00', $tz), new \DateTime('2012-09-12 01:45:00', $tz)));
-        $this->assertFalse($vfb->isFree(new \DateTime('2012-09-12 08:05:00', $tz), new \DateTime('2012-09-12 08:10:00', $tz)));
-        $this->assertFalse($vfb->isFree(new \DateTime('2012-09-12 10:15:00', $tz), new \DateTime('2012-09-12 10:45:00', $tz)));
+        self::assertFalse($vfb->isFree(new \DateTime('2012-09-12 01:15:00', $tz), new \DateTime('2012-09-12 01:45:00', $tz)));
+        self::assertFalse($vfb->isFree(new \DateTime('2012-09-12 08:05:00', $tz), new \DateTime('2012-09-12 08:10:00', $tz)));
+        self::assertFalse($vfb->isFree(new \DateTime('2012-09-12 10:15:00', $tz), new \DateTime('2012-09-12 10:45:00', $tz)));
 
         // Checking whether the end time is treated as non-inclusive
-        $this->assertTrue($vfb->isFree(new \DateTime('2012-09-12 09:00:00', $tz), new \DateTime('2012-09-12 09:15:00', $tz)));
-        $this->assertTrue($vfb->isFree(new \DateTime('2012-09-12 09:45:00', $tz), new \DateTime('2012-09-12 10:00:00', $tz)));
-        $this->assertTrue($vfb->isFree(new \DateTime('2012-09-12 11:00:00', $tz), new \DateTime('2012-09-12 12:00:00', $tz)));
+        self::assertTrue($vfb->isFree(new \DateTime('2012-09-12 09:00:00', $tz), new \DateTime('2012-09-12 09:15:00', $tz)));
+        self::assertTrue($vfb->isFree(new \DateTime('2012-09-12 09:45:00', $tz), new \DateTime('2012-09-12 10:00:00', $tz)));
+        self::assertTrue($vfb->isFree(new \DateTime('2012-09-12 11:00:00', $tz), new \DateTime('2012-09-12 12:00:00', $tz)));
     }
 
-    public function testValidate()
+    public function testValidate(): void
     {
         $input = <<<HI
 BEGIN:VCALENDAR
@@ -59,6 +59,6 @@ public function testValidate()
             $messages[] = $warning['message'];
         }
 
-        $this->assertEquals([], $messages);
+        self::assertEquals([], $messages);
     }
 }
diff --git a/tests/VObject/Component/VJournalTest.php b/tests/VObject/Component/VJournalTest.php
index 67901b71b..98f478896 100644
--- a/tests/VObject/Component/VJournalTest.php
+++ b/tests/VObject/Component/VJournalTest.php
@@ -10,12 +10,12 @@ class VJournalTest extends TestCase
     /**
      * @dataProvider timeRangeTestData
      */
-    public function testInTimeRange(VJournal $vtodo, $start, $end, $outcome)
+    public function testInTimeRange(VJournal $vtodo, \DateTime $start, \DateTime $end, bool $outcome): void
     {
-        $this->assertEquals($outcome, $vtodo->isInTimeRange($start, $end));
+        self::assertEquals($outcome, $vtodo->isInTimeRange($start, $end));
     }
 
-    public function testValidate()
+    public function testValidate(): void
     {
         $input = <<<HI
 BEGIN:VCALENDAR
@@ -36,10 +36,10 @@ public function testValidate()
             $messages[] = $warning['message'];
         }
 
-        $this->assertEquals([], $messages);
+        self::assertEquals([], $messages);
     }
 
-    public function testValidateBroken()
+    public function testValidateBroken(): void
     {
         $input = <<<HI
 BEGIN:VCALENDAR
@@ -62,13 +62,13 @@ public function testValidateBroken()
             $messages[] = $warning['message'];
         }
 
-        $this->assertEquals(
+        self::assertEquals(
             ['URL MUST NOT appear more than once in a VJOURNAL component'],
             $messages
         );
     }
 
-    public function timeRangeTestData()
+    public function timeRangeTestData(): array
     {
         $calendar = new VCalendar();
 
diff --git a/tests/VObject/Component/VTimeZoneTest.php b/tests/VObject/Component/VTimeZoneTest.php
index af9469d36..19a88cb74 100644
--- a/tests/VObject/Component/VTimeZoneTest.php
+++ b/tests/VObject/Component/VTimeZoneTest.php
@@ -7,7 +7,7 @@
 
 class VTimeZoneTest extends TestCase
 {
-    public function testValidate()
+    public function testValidate(): void
     {
         $input = <<<HI
 BEGIN:VCALENDAR
@@ -27,10 +27,10 @@ public function testValidate()
             $messages[] = $warning['message'];
         }
 
-        $this->assertEquals([], $messages);
+        self::assertEquals([], $messages);
     }
 
-    public function testGetTimeZone()
+    public function testGetTimeZone(): void
     {
         $input = <<<HI
 BEGIN:VCALENDAR
@@ -46,7 +46,7 @@ public function testGetTimeZone()
 
         $tz = new \DateTimeZone('America/Toronto');
 
-        $this->assertEquals(
+        self::assertEquals(
             $tz,
             $obj->VTIMEZONE->getTimeZone()
         );
diff --git a/tests/VObject/Component/VTodoTest.php b/tests/VObject/Component/VTodoTest.php
index d5434458a..808675b36 100644
--- a/tests/VObject/Component/VTodoTest.php
+++ b/tests/VObject/Component/VTodoTest.php
@@ -10,12 +10,12 @@ class VTodoTest extends TestCase
     /**
      * @dataProvider timeRangeTestData
      */
-    public function testInTimeRange(VTodo $vtodo, $start, $end, $outcome)
+    public function testInTimeRange(VTodo $vtodo, \DateTime $start, \DateTime $end, bool $outcome): void
     {
-        $this->assertEquals($outcome, $vtodo->isInTimeRange($start, $end));
+        self::assertEquals($outcome, $vtodo->isInTimeRange($start, $end));
     }
 
-    public function timeRangeTestData()
+    public function timeRangeTestData(): array
     {
         $tests = [];
 
@@ -64,7 +64,7 @@ public function timeRangeTestData()
         return $tests;
     }
 
-    public function testValidate()
+    public function testValidate(): void
     {
         $input = <<<HI
 BEGIN:VCALENDAR
@@ -85,10 +85,10 @@ public function testValidate()
             $messages[] = $warning['message'];
         }
 
-        $this->assertEquals([], $messages);
+        self::assertEquals([], $messages);
     }
 
-    public function testValidateInvalid()
+    public function testValidateInvalid(): void
     {
         $input = <<<HI
 BEGIN:VCALENDAR
@@ -107,13 +107,13 @@ public function testValidateInvalid()
             $messages[] = $warning['message'];
         }
 
-        $this->assertEquals([
+        self::assertEquals([
             'UID MUST appear exactly once in a VTODO component',
             'DTSTAMP MUST appear exactly once in a VTODO component',
         ], $messages);
     }
 
-    public function testValidateDUEDTSTARTMisMatch()
+    public function testValidateDueDateTimeStartMisMatch(): void
     {
         $input = <<<HI
 BEGIN:VCALENDAR
@@ -136,12 +136,12 @@ public function testValidateDUEDTSTARTMisMatch()
             $messages[] = $warning['message'];
         }
 
-        $this->assertEquals([
+        self::assertEquals([
             'The value type (DATE or DATE-TIME) must be identical for DUE and DTSTART',
         ], $messages);
     }
 
-    public function testValidateDUEbeforeDTSTART()
+    public function testValidateDueBeforeDateTimeStart(): void
     {
         $input = <<<HI
 BEGIN:VCALENDAR
@@ -164,7 +164,7 @@ public function testValidateDUEbeforeDTSTART()
             $messages[] = $warning['message'];
         }
 
-        $this->assertEquals([
+        self::assertEquals([
             'DUE must occur after DTSTART',
         ], $messages);
     }
diff --git a/tests/VObject/ComponentTest.php b/tests/VObject/ComponentTest.php
index cf3e196dc..4a247d906 100644
--- a/tests/VObject/ComponentTest.php
+++ b/tests/VObject/ComponentTest.php
@@ -8,7 +8,7 @@
 
 class ComponentTest extends TestCase
 {
-    public function testIterate()
+    public function testIterate(): void
     {
         $comp = new VCalendar([], false);
 
@@ -21,16 +21,16 @@ public function testIterate()
         $count = 0;
         foreach ($comp->children() as $key => $subcomponent) {
             ++$count;
-            $this->assertInstanceOf(Component::class, $subcomponent);
+            self::assertInstanceOf(Component::class, $subcomponent);
 
             if (2 === $count) {
-                $this->assertEquals(1, $key);
+                self::assertEquals(1, $key);
             }
         }
-        $this->assertEquals(2, $count);
+        self::assertEquals(2, $count);
     }
 
-    public function testMagicGet()
+    public function testMagicGet(): void
     {
         $comp = new VCalendar([], false);
 
@@ -40,14 +40,17 @@ public function testMagicGet()
         $sub = $comp->createComponent('VTODO');
         $comp->add($sub);
 
-        $event = $comp->vevent;
-        $this->assertInstanceOf(Component::class, $event);
-        $this->assertEquals('VEVENT', $event->name);
+        $event = $comp->VEVENT;
+        self::assertInstanceOf(Component::class, $event);
+        self::assertEquals('VEVENT', $event->name);
 
-        $this->assertNull($comp->vjournal);
+        self::assertNull($comp->VJOURNAL);
     }
 
-    public function testMagicGetGroups()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testMagicGetGroups(): void
     {
         $comp = new VCard();
 
@@ -60,19 +63,34 @@ public function testMagicGetGroups()
         $sub = $comp->createProperty('EMAIL', '3@3.com');
         $comp->add($sub);
 
-        $emails = $comp->email;
-        $this->assertEquals(3, count($emails));
+        $sub = $comp->createProperty('0.EMAIL', '0@0.com');
+        $comp->add($sub);
+
+        $emails = $comp->EMAIL;
+        self::assertCount(4, $emails);
 
         $email1 = $comp->{'group1.email'};
-        $this->assertEquals('EMAIL', $email1[0]->name);
-        $this->assertEquals('GROUP1', $email1[0]->group);
+        self::assertEquals('EMAIL', $email1[0]->name);
+        self::assertEquals('GROUP1', $email1[0]->group);
+
+        $email0 = $comp->{'0.email'};
+        self::assertEquals('EMAIL', $email0[0]->name);
+        self::assertEquals('0', $email0[0]->group);
 
+        // this is supposed to return all EMAIL properties that do not have a group
         $email3 = $comp->{'.email'};
-        $this->assertEquals('EMAIL', $email3[0]->name);
-        $this->assertEquals(null, $email3[0]->group);
+        self::assertEquals('EMAIL', $email3[0]->name);
+        self::assertEquals(null, $email3[0]->group);
+
+        // this is supposed to return all properties that do not have a group
+        $nogroupProps = $comp->{'.'};
+        self::assertGreaterThan(0, count($email3));
+        foreach ($nogroupProps as $prop) {
+            self::assertEquals(null, $prop->group);
+        }
     }
 
-    public function testAddGroupProperties()
+    public function testAddGroupProperties(): void
     {
         $comp = new VCard([
             'VERSION' => '3.0',
@@ -83,13 +101,13 @@ public function testAddGroupProperties()
 
         foreach (['item2', 'ITEM1'] as $group) {
             $prop = $comp->{"$group.X-ABLabel"};
-            $this->assertInstanceOf(Property::class, $prop);
-            $this->assertSame("$group-Foo", (string) $prop);
-            $this->assertSame($group, $prop->group);
+            self::assertInstanceOf(Property::class, $prop);
+            self::assertSame("$group-Foo", (string) $prop);
+            self::assertSame($group, $prop->group);
         }
     }
 
-    public function testMagicIsset()
+    public function testMagicIsset(): void
     {
         $comp = new VCalendar();
 
@@ -99,65 +117,65 @@ public function testMagicIsset()
         $sub = $comp->createComponent('VTODO');
         $comp->add($sub);
 
-        $this->assertTrue(isset($comp->vevent));
-        $this->assertTrue(isset($comp->vtodo));
-        $this->assertFalse(isset($comp->vjournal));
+        self::assertTrue(isset($comp->vevent));
+        self::assertTrue(isset($comp->vtodo));
+        self::assertFalse(isset($comp->vjournal));
     }
 
-    public function testMagicSetScalar()
+    public function testMagicSetScalar(): void
     {
         $comp = new VCalendar();
         $comp->myProp = 'myValue';
 
-        $this->assertInstanceOf(Property::class, $comp->MYPROP);
-        $this->assertEquals('myValue', (string) $comp->MYPROP);
+        self::assertInstanceOf(Property::class, $comp->MYPROP);
+        self::assertEquals('myValue', (string) $comp->MYPROP);
     }
 
-    public function testMagicSetScalarTwice()
+    public function testMagicSetScalarTwice(): void
     {
         $comp = new VCalendar([], false);
         $comp->myProp = 'myValue';
         $comp->myProp = 'myValue';
 
-        $this->assertEquals(1, count($comp->children()));
-        $this->assertInstanceOf(Property::class, $comp->MYPROP);
-        $this->assertEquals('myValue', (string) $comp->MYPROP);
+        self::assertCount(1, $comp->children());
+        self::assertInstanceOf(Property::class, $comp->MYPROP);
+        self::assertEquals('myValue', (string) $comp->MYPROP);
     }
 
-    public function testMagicSetArray()
+    public function testMagicSetArray(): void
     {
         $comp = new VCalendar();
         $comp->ORG = ['Acme Inc', 'Section 9'];
 
-        $this->assertInstanceOf(Property::class, $comp->ORG);
-        $this->assertEquals(['Acme Inc', 'Section 9'], $comp->ORG->getParts());
+        self::assertInstanceOf(Property::class, $comp->ORG);
+        self::assertEquals(['Acme Inc', 'Section 9'], $comp->ORG->getParts());
     }
 
-    public function testMagicSetComponent()
+    public function testMagicSetComponent(): void
     {
         $comp = new VCalendar();
 
         // Note that 'myProp' is ignored here.
         $comp->myProp = $comp->createComponent('VEVENT');
 
-        $this->assertEquals(1, count($comp));
+        self::assertCount(1, $comp);
 
-        $this->assertEquals('VEVENT', $comp->VEVENT->name);
+        self::assertEquals('VEVENT', $comp->VEVENT->name);
     }
 
-    public function testMagicSetTwice()
+    public function testMagicSetTwice(): void
     {
         $comp = new VCalendar([], false);
 
         $comp->VEVENT = $comp->createComponent('VEVENT');
         $comp->VEVENT = $comp->createComponent('VEVENT');
 
-        $this->assertEquals(1, count($comp->children()));
+        self::assertCount(1, $comp->children());
 
-        $this->assertEquals('VEVENT', $comp->VEVENT->name);
+        self::assertEquals('VEVENT', $comp->VEVENT->name);
     }
 
-    public function testArrayAccessGet()
+    public function testArrayAccessGet(): void
     {
         $comp = new VCalendar([], false);
 
@@ -171,12 +189,12 @@ public function testArrayAccessGet()
 
         $comp->add($event2);
 
-        $this->assertEquals(2, count($comp->children()));
-        $this->assertTrue($comp->vevent[1] instanceof Component);
-        $this->assertEquals('Event 2', (string) $comp->vevent[1]->summary);
+        self::assertCount(2, $comp->children());
+        self::assertTrue($comp->vevent[1] instanceof Component);
+        self::assertEquals('Event 2', (string) $comp->vevent[1]->summary);
     }
 
-    public function testArrayAccessExists()
+    public function testArrayAccessExists(): void
     {
         $comp = new VCalendar();
 
@@ -190,113 +208,113 @@ public function testArrayAccessExists()
 
         $comp->add($event2);
 
-        $this->assertTrue(isset($comp->vevent[0]));
-        $this->assertTrue(isset($comp->vevent[1]));
+        self::assertTrue(isset($comp->vevent[0]));
+        self::assertTrue(isset($comp->vevent[1]));
     }
 
-    public function testArrayAccessSet()
+    public function testArrayAccessSet(): void
     {
         $this->expectException(\LogicException::class);
         $comp = new VCalendar();
         $comp['hey'] = 'hi there';
     }
 
-    public function testArrayAccessUnset()
+    public function testArrayAccessUnset(): void
     {
         $this->expectException(\LogicException::class);
         $comp = new VCalendar();
         unset($comp[0]);
     }
 
-    public function testAddScalar()
+    public function testAddScalar(): void
     {
         $comp = new VCalendar([], false);
 
         $comp->add('myprop', 'value');
 
-        $this->assertEquals(1, count($comp->children()));
+        self::assertCount(1, $comp->children());
 
         $bla = $comp->children()[0];
 
-        $this->assertTrue($bla instanceof Property);
-        $this->assertEquals('MYPROP', $bla->name);
-        $this->assertEquals('value', (string) $bla);
+        self::assertTrue($bla instanceof Property);
+        self::assertEquals('MYPROP', $bla->name);
+        self::assertEquals('value', (string) $bla);
     }
 
-    public function testAddScalarParams()
+    public function testAddScalarParams(): void
     {
         $comp = new VCalendar([], false);
 
         $comp->add('myprop', 'value', ['param1' => 'value1']);
 
-        $this->assertEquals(1, count($comp->children()));
+        self::assertCount(1, $comp->children());
 
         $bla = $comp->children()[0];
 
-        $this->assertInstanceOf(Property::class, $bla);
-        $this->assertEquals('MYPROP', $bla->name);
-        $this->assertEquals('value', (string) $bla);
+        self::assertInstanceOf(Property::class, $bla);
+        self::assertEquals('MYPROP', $bla->name);
+        self::assertEquals('value', (string) $bla);
 
-        $this->assertEquals(1, count($bla->parameters()));
+        self::assertCount(1, $bla->parameters());
 
-        $this->assertEquals('PARAM1', $bla->parameters['PARAM1']->name);
-        $this->assertEquals('value1', $bla->parameters['PARAM1']->getValue());
+        self::assertEquals('PARAM1', $bla->parameters['PARAM1']->name);
+        self::assertEquals('value1', $bla->parameters['PARAM1']->getValue());
     }
 
-    public function testAddComponent()
+    public function testAddComponent(): void
     {
         $comp = new VCalendar([], false);
 
         $comp->add($comp->createComponent('VEVENT'));
 
-        $this->assertEquals(1, count($comp->children()));
+        self::assertCount(1, $comp->children());
 
-        $this->assertEquals('VEVENT', $comp->VEVENT->name);
+        self::assertEquals('VEVENT', $comp->VEVENT->name);
     }
 
-    public function testAddComponentTwice()
+    public function testAddComponentTwice(): void
     {
         $comp = new VCalendar([], false);
 
         $comp->add($comp->createComponent('VEVENT'));
         $comp->add($comp->createComponent('VEVENT'));
 
-        $this->assertEquals(2, count($comp->children()));
+        self::assertCount(2, $comp->children());
 
-        $this->assertEquals('VEVENT', $comp->VEVENT->name);
+        self::assertEquals('VEVENT', $comp->VEVENT->name);
     }
 
-    public function testAddArgFail()
+    public function testAddArgFail(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $comp = new VCalendar();
         $comp->add($comp->createComponent('VEVENT'), 'hello');
     }
 
-    public function testAddArgFail2()
+    public function testAddArgFail2(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $comp = new VCalendar();
         $comp->add([]);
     }
 
-    public function testMagicUnset()
+    public function testMagicUnset(): void
     {
         $comp = new VCalendar([], false);
         $comp->add($comp->createComponent('VEVENT'));
 
         unset($comp->vevent);
 
-        $this->assertEquals(0, count($comp->children()));
+        self::assertCount(0, $comp->children());
     }
 
-    public function testCount()
+    public function testCount(): void
     {
         $comp = new VCalendar();
-        $this->assertEquals(1, $comp->count());
+        self::assertEquals(1, $comp->count());
     }
 
-    public function testChildren()
+    public function testChildren(): void
     {
         $comp = new VCalendar([], false);
 
@@ -305,11 +323,14 @@ public function testChildren()
         $comp->add($comp->createComponent('VTODO'));
 
         $r = $comp->children();
-        $this->assertIsArray($r);
-        $this->assertEquals(2, count($r));
+        self::assertIsArray($r);
+        self::assertCount(2, $r);
     }
 
-    public function testGetComponents()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testGetComponents(): void
     {
         $comp = new VCalendar();
 
@@ -317,18 +338,18 @@ public function testGetComponents()
         $comp->add($comp->createComponent('VTODO'));
 
         $r = $comp->getComponents();
-        $this->assertIsArray($r);
-        $this->assertEquals(1, count($r));
-        $this->assertEquals('VTODO', $r[0]->name);
+        self::assertIsArray($r);
+        self::assertCount(1, $r);
+        self::assertEquals('VTODO', $r[0]->name);
     }
 
-    public function testSerialize()
+    public function testSerialize(): void
     {
         $comp = new VCalendar([], false);
-        $this->assertEquals("BEGIN:VCALENDAR\r\nEND:VCALENDAR\r\n", $comp->serialize());
+        self::assertEquals("BEGIN:VCALENDAR\r\nEND:VCALENDAR\r\n", $comp->serialize());
     }
 
-    public function testSerializeChildren()
+    public function testSerializeChildren(): void
     {
         $comp = new VCalendar([], false);
         $event = $comp->add($comp->createComponent('VEVENT'));
@@ -338,10 +359,10 @@ public function testSerializeChildren()
 
         $str = $comp->serialize();
 
-        $this->assertEquals("BEGIN:VCALENDAR\r\nBEGIN:VEVENT\r\nEND:VEVENT\r\nBEGIN:VTODO\r\nEND:VTODO\r\nEND:VCALENDAR\r\n", $str);
+        self::assertEquals("BEGIN:VCALENDAR\r\nBEGIN:VEVENT\r\nEND:VEVENT\r\nBEGIN:VTODO\r\nEND:VTODO\r\nEND:VCALENDAR\r\n", $str);
     }
 
-    public function testSerializeOrderCompAndProp()
+    public function testSerializeOrderCompAndProp(): void
     {
         $comp = new VCalendar([], false);
         $comp->add($event = $comp->createComponent('VEVENT'));
@@ -352,10 +373,10 @@ public function testSerializeOrderCompAndProp()
         unset($event->DTSTAMP, $event->UID);
         $str = $comp->serialize();
 
-        $this->assertEquals("BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPROP1:BLABLA\r\nBEGIN:VTIMEZONE\r\nEND:VTIMEZONE\r\nBEGIN:VEVENT\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n", $str);
+        self::assertEquals("BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPROP1:BLABLA\r\nBEGIN:VTIMEZONE\r\nEND:VTIMEZONE\r\nBEGIN:VEVENT\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n", $str);
     }
 
-    public function testAnotherSerializeOrderProp()
+    public function testAnotherSerializeOrderProp(): void
     {
         $prop4s = ['1', '2', '3', '4', '5', '6', '7', '8', '9', '10'];
 
@@ -378,21 +399,21 @@ public function testAnotherSerializeOrderProp()
 
         $str = $comp->serialize();
 
-        $this->assertEquals("BEGIN:VCARD\r\nVERSION:2.0\r\nSOMEPROP:FOO\r\nANOTHERPROP:FOO\r\nTHIRDPROP:FOO\r\nPROP4:FOO 1\r\nPROP4:FOO 2\r\nPROP4:FOO 3\r\nPROP4:FOO 4\r\nPROP4:FOO 5\r\nPROP4:FOO 6\r\nPROP4:FOO 7\r\nPROP4:FOO 8\r\nPROP4:FOO 9\r\nPROP4:FOO 10\r\nPROPNUMBERFIVE:FOO\r\nPROPNUMBERSIX:FOO\r\nPROPNUMBERSEVEN:FOO\r\nPROPNUMBEREIGHT:FOO\r\nPROPNUMBERNINE:FOO\r\nPROPNUMBERTEN:FOO\r\nUID:FOO\r\nEND:VCARD\r\n", $str);
+        self::assertEquals("BEGIN:VCARD\r\nVERSION:2.0\r\nSOMEPROP:FOO\r\nANOTHERPROP:FOO\r\nTHIRDPROP:FOO\r\nPROP4:FOO 1\r\nPROP4:FOO 2\r\nPROP4:FOO 3\r\nPROP4:FOO 4\r\nPROP4:FOO 5\r\nPROP4:FOO 6\r\nPROP4:FOO 7\r\nPROP4:FOO 8\r\nPROP4:FOO 9\r\nPROP4:FOO 10\r\nPROPNUMBERFIVE:FOO\r\nPROPNUMBERSIX:FOO\r\nPROPNUMBERSEVEN:FOO\r\nPROPNUMBEREIGHT:FOO\r\nPROPNUMBERNINE:FOO\r\nPROPNUMBERTEN:FOO\r\nUID:FOO\r\nEND:VCARD\r\n", $str);
     }
 
-    public function testInstantiateWithChildren()
+    public function testInstantiateWithChildren(): void
     {
         $comp = new VCard([
             'ORG' => ['Acme Inc.', 'Section 9'],
             'FN' => 'Finn The Human',
         ]);
 
-        $this->assertEquals(['Acme Inc.', 'Section 9'], $comp->ORG->getParts());
-        $this->assertEquals('Finn The Human', $comp->FN->getValue());
+        self::assertEquals(['Acme Inc.', 'Section 9'], $comp->ORG->getParts());
+        self::assertEquals('Finn The Human', $comp->FN->getValue());
     }
 
-    public function testInstantiateSubComponent()
+    public function testInstantiateSubComponent(): void
     {
         $comp = new VCalendar();
         $event = $comp->createComponent('VEVENT', [
@@ -400,10 +421,10 @@ public function testInstantiateSubComponent()
         ]);
         $comp->add($event);
 
-        $this->assertEquals('12345', $comp->VEVENT->UID->getValue());
+        self::assertEquals('12345', $comp->VEVENT->UID->getValue());
     }
 
-    public function testRemoveByName()
+    public function testRemoveByName(): void
     {
         $comp = new VCalendar([], false);
         $comp->add('prop1', 'val1');
@@ -411,22 +432,25 @@ public function testRemoveByName()
         $comp->add('prop2', 'val2');
 
         $comp->remove('prop2');
-        $this->assertFalse(isset($comp->prop2));
-        $this->assertTrue(isset($comp->prop1));
+        self::assertFalse(isset($comp->prop2));
+        self::assertTrue(isset($comp->prop1));
     }
 
-    public function testRemoveByObj()
+    public function testRemoveByObj(): void
     {
         $comp = new VCalendar([], false);
         $comp->add('prop1', 'val1');
         $prop = $comp->add('prop2', 'val2');
 
         $comp->remove($prop);
-        $this->assertFalse(isset($comp->prop2));
-        $this->assertTrue(isset($comp->prop1));
+        self::assertFalse(isset($comp->prop2));
+        self::assertTrue(isset($comp->prop1));
     }
 
-    public function testRemoveNotFound()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testRemoveNotFound(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $comp = new VCalendar([], false);
@@ -437,28 +461,28 @@ public function testRemoveNotFound()
     /**
      * @dataProvider ruleData
      */
-    public function testValidateRules($componentList, $errorCount)
+    public function testValidateRules(array $componentList, int $errorCount): void
     {
         $vcard = new Component\VCard();
 
-        $component = new FakeComponent($vcard, 'Hi', [], $defaults = false);
+        $component = new FakeComponent($vcard, 'Hi', [], false);
         foreach ($componentList as $v) {
             $component->add($v, 'Hello.');
         }
 
-        $this->assertEquals($errorCount, count($component->validate()));
+        self::assertCount($errorCount, $component->validate());
     }
 
-    public function testValidateRepair()
+    public function testValidateRepair(): void
     {
         $vcard = new Component\VCard();
 
-        $component = new FakeComponent($vcard, 'Hi', [], $defaults = false);
+        $component = new FakeComponent($vcard, 'Hi', [], false);
         $component->validate(Component::REPAIR);
-        $this->assertEquals('yow', $component->BAR->getValue());
+        self::assertEquals('yow', $component->BAR->getValue());
     }
 
-    public function testValidateRepairShouldNotDeduplicatePropertiesWhenValuesDiffer()
+    public function testValidateRepairShouldNotDeduplicatePropertiesWhenValuesDiffer(): void
     {
         $vcard = new Component\VCard();
 
@@ -469,12 +493,12 @@ public function testValidateRepairShouldNotDeduplicatePropertiesWhenValuesDiffer
 
         $messages = $component->validate(Component::REPAIR);
 
-        $this->assertEquals(1, count($messages));
-        $this->assertEquals(3, $messages[0]['level']);
-        $this->assertEquals(2, count($component->GIR));
+        self::assertCount(1, $messages);
+        self::assertEquals(3, $messages[0]['level']);
+        self::assertCount(2, $component->GIR);
     }
 
-    public function testValidateRepairShouldNotDeduplicatePropertiesWhenParametersDiffer()
+    public function testValidateRepairShouldNotDeduplicatePropertiesWhenParametersDiffer(): void
     {
         $vcard = new Component\VCard();
 
@@ -485,12 +509,12 @@ public function testValidateRepairShouldNotDeduplicatePropertiesWhenParametersDi
 
         $messages = $component->validate(Component::REPAIR);
 
-        $this->assertEquals(1, count($messages));
-        $this->assertEquals(3, $messages[0]['level']);
-        $this->assertEquals(2, count($component->GIR));
+        self::assertCount(1, $messages);
+        self::assertEquals(3, $messages[0]['level']);
+        self::assertCount(2, $component->GIR);
     }
 
-    public function testValidateRepairShouldDeduplicatePropertiesWhenValuesAndParametersAreEqual()
+    public function testValidateRepairShouldDeduplicatePropertiesWhenValuesAndParametersAreEqual(): void
     {
         $vcard = new Component\VCard();
 
@@ -501,12 +525,12 @@ public function testValidateRepairShouldDeduplicatePropertiesWhenValuesAndParame
 
         $messages = $component->validate(Component::REPAIR);
 
-        $this->assertEquals(1, count($messages));
-        $this->assertEquals(1, $messages[0]['level']);
-        $this->assertEquals(1, count($component->GIR));
+        self::assertCount(1, $messages);
+        self::assertEquals(1, $messages[0]['level']);
+        self::assertCount(1, $component->GIR);
     }
 
-    public function testValidateRepairShouldDeduplicatePropertiesWhenValuesAreEqual()
+    public function testValidateRepairShouldDeduplicatePropertiesWhenValuesAreEqual(): void
     {
         $vcard = new Component\VCard();
 
@@ -517,12 +541,12 @@ public function testValidateRepairShouldDeduplicatePropertiesWhenValuesAreEqual(
 
         $messages = $component->validate(Component::REPAIR);
 
-        $this->assertEquals(1, count($messages));
-        $this->assertEquals(1, $messages[0]['level']);
-        $this->assertEquals(1, count($component->GIR));
+        self::assertCount(1, $messages);
+        self::assertEquals(1, $messages[0]['level']);
+        self::assertCount(1, $component->GIR);
     }
 
-    public function ruleData()
+    public function ruleData(): array
     {
         return [
             [[], 2],
@@ -539,7 +563,7 @@ public function ruleData()
 
 class FakeComponent extends Component
 {
-    public function getValidationRules()
+    public function getValidationRules(): array
     {
         return [
             'FOO' => '0',
@@ -550,7 +574,7 @@ public function getValidationRules()
         ];
     }
 
-    public function getDefaults()
+    public function getDefaults(): array
     {
         return [
             'BAR' => 'yow',
diff --git a/tests/VObject/DateTimeParserTest.php b/tests/VObject/DateTimeParserTest.php
index ede81e321..cdf0fe990 100644
--- a/tests/VObject/DateTimeParserTest.php
+++ b/tests/VObject/DateTimeParserTest.php
@@ -2,185 +2,194 @@
 
 namespace Sabre\VObject;
 
-use DateInterval;
-use DateTimeImmutable;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 
 class DateTimeParserTest extends TestCase
 {
-    public function testParseICalendarDuration()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testParseICalendarDuration(): void
     {
-        $this->assertEquals('+1 weeks', DateTimeParser::parseDuration('P1W', true));
-        $this->assertEquals('+5 days', DateTimeParser::parseDuration('P5D', true));
-        $this->assertEquals('+5 days 3 hours 50 minutes 12 seconds', DateTimeParser::parseDuration('P5DT3H50M12S', true));
-        $this->assertEquals('-1 weeks 50 minutes', DateTimeParser::parseDuration('-P1WT50M', true));
-        $this->assertEquals('+50 days 3 hours 2 seconds', DateTimeParser::parseDuration('+P50DT3H2S', true));
-        $this->assertEquals('+0 seconds', DateTimeParser::parseDuration('+PT0S', true));
-        $this->assertEquals(new DateInterval('PT0S'), DateTimeParser::parseDuration('PT0S'));
+        self::assertEquals('+1 weeks', DateTimeParser::parseDurationAsString('P1W'));
+        self::assertEquals('+5 days', DateTimeParser::parseDurationAsString('P5D'));
+        self::assertEquals('+5 days 3 hours 50 minutes 12 seconds', DateTimeParser::parseDurationAsString('P5DT3H50M12S'));
+        self::assertEquals('-1 weeks 50 minutes', DateTimeParser::parseDurationAsString('-P1WT50M'));
+        self::assertEquals('+50 days 3 hours 2 seconds', DateTimeParser::parseDurationAsString('+P50DT3H2S'));
+        self::assertEquals('+0 seconds', DateTimeParser::parseDurationAsString('+PT0S'));
+        self::assertEquals(new \DateInterval('PT0S'), DateTimeParser::parseDuration('PT0S'));
     }
 
-    public function testParseICalendarDurationDateInterval()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testParseICalendarDurationDateInterval(): void
     {
-        $expected = new DateInterval('P7D');
-        $this->assertEquals($expected, DateTimeParser::parseDuration('P1W'));
-        $this->assertEquals($expected, DateTimeParser::parse('P1W'));
+        $expected = new \DateInterval('P7D');
+        self::assertEquals($expected, DateTimeParser::parseDuration('P1W'));
+        self::assertEquals($expected, DateTimeParser::parse('P1W'));
 
-        $expected = new DateInterval('PT3M');
+        $expected = new \DateInterval('PT3M');
         $expected->invert = true;
-        $this->assertEquals($expected, DateTimeParser::parseDuration('-PT3M'));
+        self::assertEquals($expected, DateTimeParser::parseDuration('-PT3M'));
+    }
+
+    public function testParseDurationZero(): void
+    {
+        $expected = new \DateInterval('PT0S');
+        self::assertEquals($expected, DateTimeParser::parseDuration('P'));
     }
 
-    public function testParseICalendarDurationFail()
+    public function testParseICalendarDurationFail(): void
     {
         $this->expectException(InvalidDataException::class);
-        DateTimeParser::parseDuration('P1X', true);
+        DateTimeParser::parseDurationAsString('P1X');
     }
 
-    public function testParseICalendarDateTime()
+    public function testParseICalendarDateTime(): void
     {
         $dateTime = DateTimeParser::parseDateTime('20100316T141405');
 
-        $compare = new DateTimeImmutable('2010-03-16 14:14:05', new DateTimeZone('UTC'));
+        $compare = new \DateTimeImmutable('2010-03-16 14:14:05', new \DateTimeZone('UTC'));
 
-        $this->assertEquals($compare, $dateTime);
+        self::assertEquals($compare, $dateTime);
     }
 
     /**
      * @depends testParseICalendarDateTime
      */
-    public function testParseICalendarDateTimeBadFormat()
+    public function testParseICalendarDateTimeBadFormat(): void
     {
         $this->expectException(InvalidDataException::class);
-        $dateTime = DateTimeParser::parseDateTime('20100316T141405 ');
+        DateTimeParser::parseDateTime('20100316T141405 ');
     }
 
     /**
      * @depends testParseICalendarDateTime
      */
-    public function testParseICalendarDateTimeInvalidTime()
+    public function testParseICalendarDateTimeInvalidTime(): void
     {
         $this->expectException(InvalidDataException::class);
-        $dateTime = DateTimeParser::parseDateTime('20100316T251405');
+        DateTimeParser::parseDateTime('20100316T251405');
     }
 
     /**
      * @depends testParseICalendarDateTime
      */
-    public function testParseICalendarDateTimeUTC()
+    public function testParseICalendarDateTimeUTC(): void
     {
         $dateTime = DateTimeParser::parseDateTime('20100316T141405Z');
 
-        $compare = new DateTimeImmutable('2010-03-16 14:14:05', new DateTimeZone('UTC'));
-        $this->assertEquals($compare, $dateTime);
+        $compare = new \DateTimeImmutable('2010-03-16 14:14:05', new \DateTimeZone('UTC'));
+        self::assertEquals($compare, $dateTime);
     }
 
     /**
      * @depends testParseICalendarDateTime
      */
-    public function testParseICalendarDateTimeUTC2()
+    public function testParseICalendarDateTimeUTC2(): void
     {
         $dateTime = DateTimeParser::parseDateTime('20101211T160000Z');
 
-        $compare = new DateTimeImmutable('2010-12-11 16:00:00', new DateTimeZone('UTC'));
-        $this->assertEquals($compare, $dateTime);
+        $compare = new \DateTimeImmutable('2010-12-11 16:00:00', new \DateTimeZone('UTC'));
+        self::assertEquals($compare, $dateTime);
     }
 
     /**
      * @depends testParseICalendarDateTime
      */
-    public function testParseICalendarDateTimeCustomTimeZone()
+    public function testParseICalendarDateTimeCustomTimeZone(): void
     {
-        $dateTime = DateTimeParser::parseDateTime('20100316T141405', new DateTimeZone('Europe/Amsterdam'));
+        $dateTime = DateTimeParser::parseDateTime('20100316T141405', new \DateTimeZone('Europe/Amsterdam'));
 
-        $compare = new DateTimeImmutable('2010-03-16 14:14:05', new DateTimeZone('Europe/Amsterdam'));
-        $this->assertEquals($compare, $dateTime);
+        $compare = new \DateTimeImmutable('2010-03-16 14:14:05', new \DateTimeZone('Europe/Amsterdam'));
+        self::assertEquals($compare, $dateTime);
     }
 
-    public function testParseICalendarDate()
+    public function testParseICalendarDate(): void
     {
         $dateTime = DateTimeParser::parseDate('20100316');
 
-        $expected = new DateTimeImmutable('2010-03-16 00:00:00', new DateTimeZone('UTC'));
+        $expected = new \DateTimeImmutable('2010-03-16 00:00:00', new \DateTimeZone('UTC'));
 
-        $this->assertEquals($expected, $dateTime);
+        self::assertEquals($expected, $dateTime);
 
         $dateTime = DateTimeParser::parse('20100316');
-        $this->assertEquals($expected, $dateTime);
+        self::assertEquals($expected, $dateTime);
     }
 
     /**
      * TCheck if a date with year > 4000 will not throw an exception. iOS seems to use 45001231 in yearly recurring events.
      */
-    public function testParseICalendarDateGreaterThan4000()
+    public function testParseICalendarDateGreaterThan4000(): void
     {
         $dateTime = DateTimeParser::parseDate('45001231');
 
-        $expected = new DateTimeImmutable('4500-12-31 00:00:00', new DateTimeZone('UTC'));
+        $expected = new \DateTimeImmutable('4500-12-31 00:00:00', new \DateTimeZone('UTC'));
 
-        $this->assertEquals($expected, $dateTime);
+        self::assertEquals($expected, $dateTime);
 
         $dateTime = DateTimeParser::parse('45001231');
-        $this->assertEquals($expected, $dateTime);
+        self::assertEquals($expected, $dateTime);
     }
 
     /**
      * Check if a datetime with year > 4000 will not throw an exception. iOS seems to use 45001231T235959 in yearly recurring events.
      */
-    public function testParseICalendarDateTimeGreaterThan4000()
+    public function testParseICalendarDateTimeGreaterThan4000(): void
     {
         $dateTime = DateTimeParser::parseDateTime('45001231T235959');
 
-        $expected = new DateTimeImmutable('4500-12-31 23:59:59', new DateTimeZone('UTC'));
+        $expected = new \DateTimeImmutable('4500-12-31 23:59:59', new \DateTimeZone('UTC'));
 
-        $this->assertEquals($expected, $dateTime);
+        self::assertEquals($expected, $dateTime);
 
         $dateTime = DateTimeParser::parse('45001231T235959');
-        $this->assertEquals($expected, $dateTime);
+        self::assertEquals($expected, $dateTime);
     }
 
     /**
      * @depends testParseICalendarDate
      */
-    public function testParseICalendarDateBadFormat()
+    public function testParseICalendarDateBadFormat(): void
     {
         $this->expectException(InvalidDataException::class);
-        $dateTime = DateTimeParser::parseDate('20100316T141405');
+        DateTimeParser::parseDate('20100316T141405');
     }
 
     /**
      * @depends testParseICalendarDate
      */
-    public function testParseICalendarDateInvalidDate()
+    public function testParseICalendarDateInvalidDate(): void
     {
         $this->expectException(InvalidDataException::class);
-        $dateTime = DateTimeParser::parseDate('20101331');
+        DateTimeParser::parseDate('20101331');
     }
 
     /**
      * @dataProvider vcardDates
      */
-    public function testVCardDate($input, $output)
+    public function testVCardDate(string $input, array $output): void
     {
-        $this->assertEquals(
+        self::assertEquals(
             $output,
             DateTimeParser::parseVCardDateTime($input)
         );
     }
 
-    public function testBadVCardDate()
+    public function testBadVCardDate(): void
     {
         $this->expectException(InvalidDataException::class);
         DateTimeParser::parseVCardDateTime('1985---01');
     }
 
-    public function testBadVCardTime()
+    public function testBadVCardTime(): void
     {
         $this->expectException(InvalidDataException::class);
         DateTimeParser::parseVCardTime('23:12:166');
     }
 
-    public function vcardDates()
+    public function vcardDates(): array
     {
         return [
             [
@@ -408,9 +417,9 @@ public function vcardDates()
         ];
     }
 
-    public function testDateAndOrTimeDateWithYearMonthDay()
+    public function testDateAndOrTimeDateWithYearMonthDay(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '20150128',
             [
                 'year' => '2015',
@@ -420,9 +429,9 @@ public function testDateAndOrTimeDateWithYearMonthDay()
         );
     }
 
-    public function testDateAndOrTimeDateWithYearMonth()
+    public function testDateAndOrTimeDateWithYearMonth(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '2015-01',
             [
                 'year' => '2015',
@@ -431,9 +440,9 @@ public function testDateAndOrTimeDateWithYearMonth()
         );
     }
 
-    public function testDateAndOrTimeDateWithMonth()
+    public function testDateAndOrTimeDateWithMonth(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '--01',
             [
                 'month' => '01',
@@ -441,9 +450,9 @@ public function testDateAndOrTimeDateWithMonth()
         );
     }
 
-    public function testDateAndOrTimeDateWithMonthDay()
+    public function testDateAndOrTimeDateWithMonthDay(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '--0128',
             [
                 'month' => '01',
@@ -452,9 +461,9 @@ public function testDateAndOrTimeDateWithMonthDay()
         );
     }
 
-    public function testDateAndOrTimeDateWithDay()
+    public function testDateAndOrTimeDateWithDay(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '---28',
             [
                 'date' => '28',
@@ -462,9 +471,9 @@ public function testDateAndOrTimeDateWithDay()
         );
     }
 
-    public function testDateAndOrTimeTimeWithHour()
+    public function testDateAndOrTimeTimeWithHour(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '13',
             [
                 'hour' => '13',
@@ -472,9 +481,9 @@ public function testDateAndOrTimeTimeWithHour()
         );
     }
 
-    public function testDateAndOrTimeTimeWithHourMinute()
+    public function testDateAndOrTimeTimeWithHourMinute(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '1353',
             [
                 'hour' => '13',
@@ -483,9 +492,9 @@ public function testDateAndOrTimeTimeWithHourMinute()
         );
     }
 
-    public function testDateAndOrTimeTimeWithHourSecond()
+    public function testDateAndOrTimeTimeWithHourSecond(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '135301',
             [
                 'hour' => '13',
@@ -495,9 +504,9 @@ public function testDateAndOrTimeTimeWithHourSecond()
         );
     }
 
-    public function testDateAndOrTimeTimeWithMinute()
+    public function testDateAndOrTimeTimeWithMinute(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '-53',
             [
                 'minute' => '53',
@@ -505,9 +514,9 @@ public function testDateAndOrTimeTimeWithMinute()
         );
     }
 
-    public function testDateAndOrTimeTimeWithMinuteSecond()
+    public function testDateAndOrTimeTimeWithMinuteSecond(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '-5301',
             [
                 'minute' => '53',
@@ -516,9 +525,9 @@ public function testDateAndOrTimeTimeWithMinuteSecond()
         );
     }
 
-    public function testDateAndOrTimeTimeWithSecond()
+    public function testDateAndOrTimeTimeWithSecond(): void
     {
-        $this->assertTrue(true);
+        self::assertTrue(true);
 
         /*
          * This is unreachable due to a conflict between date and time pattern.
@@ -526,9 +535,9 @@ public function testDateAndOrTimeTimeWithSecond()
          */
     }
 
-    public function testDateAndOrTimeTimeWithSecondZ()
+    public function testDateAndOrTimeTimeWithSecondZ(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '--01Z',
             [
                 'second' => '01',
@@ -537,9 +546,9 @@ public function testDateAndOrTimeTimeWithSecondZ()
         );
     }
 
-    public function testDateAndOrTimeTimeWithSecondTZ()
+    public function testDateAndOrTimeTimeWithSecondTZ(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '--01+1234',
             [
                 'second' => '01',
@@ -548,9 +557,9 @@ public function testDateAndOrTimeTimeWithSecondTZ()
         );
     }
 
-    public function testDateAndOrTimeDateTimeWithYearMonthDayHour()
+    public function testDateAndOrTimeDateTimeWithYearMonthDayHour(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '20150128T13',
             [
                 'year' => '2015',
@@ -561,9 +570,9 @@ public function testDateAndOrTimeDateTimeWithYearMonthDayHour()
         );
     }
 
-    public function testDateAndOrTimeDateTimeWithMonthDayHour()
+    public function testDateAndOrTimeDateTimeWithMonthDayHour(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '--0128T13',
             [
                 'month' => '01',
@@ -573,9 +582,9 @@ public function testDateAndOrTimeDateTimeWithMonthDayHour()
         );
     }
 
-    public function testDateAndOrTimeDateTimeWithDayHour()
+    public function testDateAndOrTimeDateTimeWithDayHour(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '---28T13',
             [
                 'date' => '28',
@@ -584,9 +593,9 @@ public function testDateAndOrTimeDateTimeWithDayHour()
         );
     }
 
-    public function testDateAndOrTimeDateTimeWithDayHourMinute()
+    public function testDateAndOrTimeDateTimeWithDayHourMinute(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '---28T1353',
             [
                 'date' => '28',
@@ -596,9 +605,9 @@ public function testDateAndOrTimeDateTimeWithDayHourMinute()
         );
     }
 
-    public function testDateAndOrTimeDateTimeWithDayHourMinuteSecond()
+    public function testDateAndOrTimeDateTimeWithDayHourMinuteSecond(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '---28T135301',
             [
                 'date' => '28',
@@ -609,9 +618,9 @@ public function testDateAndOrTimeDateTimeWithDayHourMinuteSecond()
         );
     }
 
-    public function testDateAndOrTimeDateTimeWithDayHourZ()
+    public function testDateAndOrTimeDateTimeWithDayHourZ(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '---28T13Z',
             [
                 'date' => '28',
@@ -621,9 +630,9 @@ public function testDateAndOrTimeDateTimeWithDayHourZ()
         );
     }
 
-    public function testDateAndOrTimeDateTimeWithDayHourTZ()
+    public function testDateAndOrTimeDateTimeWithDayHourTZ(): void
     {
-        $this->assertDateAndOrTimeEqualsTo(
+        self::assertDateAndOrTimeEqualsTo(
             '---28T13+1234',
             [
                 'date' => '28',
@@ -633,9 +642,9 @@ public function testDateAndOrTimeDateTimeWithDayHourTZ()
         );
     }
 
-    protected function assertDateAndOrTimeEqualsTo($date, $parts)
+    protected function assertDateAndOrTimeEqualsTo(string $date, array $parts): void
     {
-        $this->assertSame(
+        self::assertSame(
             DateTimeParser::parseVCardDateAndOrTime($date),
             array_merge(
                 [
diff --git a/tests/VObject/DocumentTest.php b/tests/VObject/DocumentTest.php
index f2698f65f..d03a88836 100644
--- a/tests/VObject/DocumentTest.php
+++ b/tests/VObject/DocumentTest.php
@@ -6,29 +6,29 @@
 
 class DocumentTest extends TestCase
 {
-    public function testGetDocumentType()
+    public function testGetDocumentType(): void
     {
-        $doc = new MockDocument();
-        $this->assertEquals(Document::UNKNOWN, $doc->getDocumentType());
+        $doc = new MockDocument('WHATEVER');
+        self::assertEquals(Document::UNKNOWN, $doc->getDocumentType());
     }
 
-    public function testConstruct()
+    public function testConstruct(): void
     {
         $doc = new MockDocument('VLIST');
-        $this->assertEquals('VLIST', $doc->name);
+        self::assertEquals('VLIST', $doc->name);
     }
 
-    public function testCreateComponent()
+    public function testCreateComponent(): void
     {
         $vcal = new Component\VCalendar([], false);
 
         $event = $vcal->createComponent('VEVENT');
 
-        $this->assertInstanceOf(Component\VEvent::class, $event);
+        self::assertInstanceOf(Component\VEvent::class, $event);
         $vcal->add($event);
 
         $prop = $vcal->createProperty('X-PROP', '1234256', ['X-PARAM' => '3']);
-        $this->assertInstanceOf(Property::class, $prop);
+        self::assertInstanceOf(Property::class, $prop);
 
         $event->add($prop);
 
@@ -38,44 +38,47 @@ public function testCreateComponent()
         );
 
         $out = $vcal->serialize();
-        $this->assertEquals("BEGIN:VCALENDAR\r\nBEGIN:VEVENT\r\nX-PROP;X-PARAM=3:1234256\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n", $out);
+        self::assertEquals("BEGIN:VCALENDAR\r\nBEGIN:VEVENT\r\nX-PROP;X-PARAM=3:1234256\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n", $out);
     }
 
-    public function testCreate()
+    public function testCreate(): void
     {
         $vcal = new Component\VCalendar([], false);
 
         $event = $vcal->create('VEVENT');
-        $this->assertInstanceOf(Component\VEvent::class, $event);
+        self::assertInstanceOf(Component\VEvent::class, $event);
 
         $prop = $vcal->create('CALSCALE');
-        $this->assertInstanceOf(Property\Text::class, $prop);
+        self::assertInstanceOf(Property\Text::class, $prop);
     }
 
-    public function testGetClassNameForPropertyValue()
+    public function testGetClassNameForPropertyValue(): void
     {
         $vcal = new Component\VCalendar([], false);
-        $this->assertEquals(Property\Text::class, $vcal->getClassNameForPropertyValue('TEXT'));
-        $this->assertNull($vcal->getClassNameForPropertyValue('FOO'));
+        self::assertEquals(Property\Text::class, $vcal->getClassNameForPropertyValue('TEXT'));
+        self::assertNull($vcal->getClassNameForPropertyValue('FOO'));
     }
 
-    public function testDestroy()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testDestroy(): void
     {
         $vcal = new Component\VCalendar([], false);
         $event = $vcal->createComponent('VEVENT');
 
-        $this->assertInstanceOf(Component\VEvent::class, $event);
+        self::assertInstanceOf(Component\VEvent::class, $event);
         $vcal->add($event);
 
         $prop = $vcal->createProperty('X-PROP', '1234256', ['X-PARAM' => '3']);
 
         $event->add($prop);
 
-        $this->assertEquals($event, $prop->parent);
+        self::assertEquals($event, $prop->parent);
 
         $vcal->destroy();
 
-        $this->assertNull($prop->parent);
+        self::assertNull($prop->parent);
     }
 }
 
diff --git a/tests/VObject/ElementListTest.php b/tests/VObject/ElementListTest.php
index f3bb8f2bb..22b616fb9 100644
--- a/tests/VObject/ElementListTest.php
+++ b/tests/VObject/ElementListTest.php
@@ -6,7 +6,7 @@
 
 class ElementListTest extends TestCase
 {
-    public function testIterate()
+    public function testIterate(): void
     {
         $cal = new Component\VCalendar();
         $sub = $cal->createComponent('VEVENT');
@@ -22,12 +22,12 @@ public function testIterate()
         $count = 0;
         foreach ($elemList as $key => $subcomponent) {
             ++$count;
-            $this->assertInstanceOf(Component::class, $subcomponent);
+            self::assertInstanceOf(Component::class, $subcomponent);
 
             if (3 === $count) {
-                $this->assertEquals(2, $key);
+                self::assertEquals(2, $key);
             }
         }
-        $this->assertEquals(3, $count);
+        self::assertEquals(3, $count);
     }
 }
diff --git a/tests/VObject/EmClientTest.php b/tests/VObject/EmClientTest.php
index bb586ba97..0af6fdb2f 100644
--- a/tests/VObject/EmClientTest.php
+++ b/tests/VObject/EmClientTest.php
@@ -2,12 +2,11 @@
 
 namespace Sabre\VObject;
 
-use DateTimeImmutable;
 use PHPUnit\Framework\TestCase;
 
 class EmClientTest extends TestCase
 {
-    public function testParseTz()
+    public function testParseTz(): void
     {
         $str = 'BEGIN:VCALENDAR
 X-WR-CALNAME:Blackhawks Schedule 2011-12
@@ -50,6 +49,6 @@ public function testParseTz()
 
         $vObject = Reader::read($str);
         $dt = $vObject->VEVENT->DTSTART->getDateTime();
-        $this->assertEquals(new DateTimeImmutable('2011-10-08 19:30:00', new \DateTimeZone('America/Chicago')), $dt);
+        self::assertEquals(new \DateTimeImmutable('2011-10-08 19:30:00', new \DateTimeZone('America/Chicago')), $dt);
     }
 }
diff --git a/tests/VObject/EmptyParameterTest.php b/tests/VObject/EmptyParameterTest.php
index 52fe878e2..6739f104a 100644
--- a/tests/VObject/EmptyParameterTest.php
+++ b/tests/VObject/EmptyParameterTest.php
@@ -6,7 +6,7 @@
 
 class EmptyParameterTest extends TestCase
 {
-    public function testRead()
+    public function testRead(): void
     {
         $input = <<<VCF
 BEGIN:VCARD
@@ -20,14 +20,14 @@ public function testRead()
 
         $vcard = Reader::read($input);
 
-        $this->assertInstanceOf(Component\VCard::class, $vcard);
-        $vcard = $vcard->convert(\Sabre\VObject\Document::VCARD30);
+        self::assertInstanceOf(Component\VCard::class, $vcard);
+        $vcard = $vcard->convert(Document::VCARD30);
         $vcard = $vcard->serialize();
 
         $converted = Reader::read($vcard);
         $converted->validate();
 
-        $this->assertTrue(isset($converted->EMAIL['X-INTERN']));
+        self::assertTrue(isset($converted->EMAIL['X-INTERN']));
 
         $version = Version::VERSION;
 
@@ -43,10 +43,10 @@ public function testRead()
 
 VCF;
 
-        $this->assertEquals($expected, str_replace("\r", '', $vcard));
+        self::assertEquals($expected, str_replace("\r", '', $vcard));
     }
 
-    public function testVCard21Parameter()
+    public function testVCard21Parameter(): void
     {
         $vcard = new Component\VCard([], false);
         $vcard->VERSION = '2.1';
@@ -64,6 +64,6 @@ public function testVCard21Parameter()
             '',
         ];
 
-        $this->assertEquals(implode("\r\n", $expected), $result);
+        self::assertEquals(implode("\r\n", $expected), $result);
     }
 }
diff --git a/tests/VObject/EmptyValueIssueTest.php b/tests/VObject/EmptyValueIssueTest.php
index 0798d9c4a..533ac6ab6 100644
--- a/tests/VObject/EmptyValueIssueTest.php
+++ b/tests/VObject/EmptyValueIssueTest.php
@@ -11,7 +11,7 @@
  */
 class EmptyValueIssueTest extends TestCase
 {
-    public function testDecodeValue()
+    public function testDecodeValue(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -25,6 +25,6 @@ public function testDecodeValue()
         $vobj = Reader::read($input);
 
         // Before this bug was fixed, getValue() would return nothing.
-        $this->assertEquals("This is a description\nwith a linebreak and a ; , and :", $vobj->VEVENT->DESCRIPTION->getValue());
+        self::assertEquals("This is a description\nwith a linebreak and a ; , and :", $vobj->VEVENT->DESCRIPTION->getValue());
     }
 }
diff --git a/tests/VObject/FreeBusyDataTest.php b/tests/VObject/FreeBusyDataTest.php
index 9e5143f65..10b2f403f 100644
--- a/tests/VObject/FreeBusyDataTest.php
+++ b/tests/VObject/FreeBusyDataTest.php
@@ -6,11 +6,11 @@
 
 class FreeBusyDataTest extends TestCase
 {
-    public function testGetData()
+    public function testGetData(): void
     {
         $fb = new FreeBusyData(100, 200);
 
-        $this->assertEquals(
+        self::assertEquals(
             [
                 [
                     'start' => 100,
@@ -25,14 +25,14 @@ public function testGetData()
     /**
      * @depends testGetData
      */
-    public function testAddBeginning()
+    public function testAddBeginning(): void
     {
         $fb = new FreeBusyData(100, 200);
 
         // Overwriting the first half
         $fb->add(100, 150, 'BUSY');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
                 [
                     'start' => 100,
@@ -51,7 +51,7 @@ public function testAddBeginning()
         // Overwriting the first half again
         $fb->add(100, 150, 'BUSY-TENTATIVE');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
                 [
                     'start' => 100,
@@ -71,14 +71,14 @@ public function testAddBeginning()
     /**
      * @depends testAddBeginning
      */
-    public function testAddEnd()
+    public function testAddEnd(): void
     {
         $fb = new FreeBusyData(100, 200);
 
         // Overwriting the first half
         $fb->add(150, 200, 'BUSY');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
                 [
                     'start' => 100,
@@ -98,14 +98,14 @@ public function testAddEnd()
     /**
      * @depends testAddEnd
      */
-    public function testAddMiddle()
+    public function testAddMiddle(): void
     {
         $fb = new FreeBusyData(100, 200);
 
         // Overwriting the first half
         $fb->add(150, 160, 'BUSY');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
                 [
                     'start' => 100,
@@ -130,14 +130,14 @@ public function testAddMiddle()
     /**
      * @depends testAddMiddle
      */
-    public function testAddMultiple()
+    public function testAddMultiple(): void
     {
         $fb = new FreeBusyData(100, 200);
 
         $fb->add(110, 120, 'BUSY');
         $fb->add(130, 140, 'BUSY');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
                 [
                     'start' => 100,
@@ -172,14 +172,14 @@ public function testAddMultiple()
     /**
      * @depends testAddMultiple
      */
-    public function testAddMultipleOverlap()
+    public function testAddMultipleOverlap(): void
     {
         $fb = new FreeBusyData(100, 200);
 
         $fb->add(110, 120, 'BUSY');
         $fb->add(130, 140, 'BUSY');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
                 [
                     'start' => 100,
@@ -212,7 +212,7 @@ public function testAddMultipleOverlap()
 
         $fb->add(115, 135, 'BUSY-TENTATIVE');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
                 [
                     'start' => 100,
@@ -247,14 +247,14 @@ public function testAddMultipleOverlap()
     /**
      * @depends testAddMultipleOverlap
      */
-    public function testAddMultipleOverlapAndMerge()
+    public function testAddMultipleOverlapAndMerge(): void
     {
         $fb = new FreeBusyData(100, 200);
 
         $fb->add(110, 120, 'BUSY');
         $fb->add(130, 140, 'BUSY');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
                 [
                     'start' => 100,
@@ -287,7 +287,7 @@ public function testAddMultipleOverlapAndMerge()
 
         $fb->add(115, 135, 'BUSY');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
                 [
                     'start' => 100,
diff --git a/tests/VObject/FreeBusyGeneratorTest.php b/tests/VObject/FreeBusyGeneratorTest.php
index 4700a2800..47283eafb 100644
--- a/tests/VObject/FreeBusyGeneratorTest.php
+++ b/tests/VObject/FreeBusyGeneratorTest.php
@@ -8,7 +8,7 @@ class FreeBusyGeneratorTest extends TestCase
 {
     use PHPUnitAssertions;
 
-    public function testGeneratorBaseObject()
+    public function testGeneratorBaseObject(): void
     {
         $obj = new Component\VCalendar();
         $obj->METHOD = 'PUBLISH';
@@ -19,13 +19,13 @@ public function testGeneratorBaseObject()
 
         $result = $gen->getResult();
 
-        $this->assertEquals('PUBLISH', $result->METHOD->getValue());
+        self::assertEquals('PUBLISH', $result->METHOD->getValue());
     }
 
-    public function testInvalidArg()
+    public function testInvalidArg(): void
     {
         $this->expectException(\InvalidArgumentException::class);
-        $gen = new FreeBusyGenerator(
+        new FreeBusyGenerator(
             new \DateTime('2012-01-01'),
             new \DateTime('2012-12-31'),
             new \stdClass()
@@ -42,12 +42,11 @@ public function testInvalidArg()
      * It only generates the freebusy report for the following time-range:
      * 2011-01-01 11:00:00 until 2011-01-03 11:11:11
      *
-     * @param string      $expected
-     * @param array       $input
-     * @param string|null $timeZone
-     * @param string      $vavailability
+     * @param array|string $input
+     *
+     * @throws ParseException
      */
-    public function assertFreeBusyReport($expected, $input, $timeZone = null, $vavailability = null)
+    public function assertFreeBusyReport(string $expected, $input, \DateTimeZone $timeZone = null, string $vavailability = null): void
     {
         $gen = new FreeBusyGenerator(
             new \DateTime('20110101T110000Z', new \DateTimeZone('UTC')),
@@ -79,10 +78,10 @@ public function assertFreeBusyReport($expected, $input, $timeZone = null, $vavai
 END:VCALENDAR
 ICS;
 
-        $this->assertVObjectEqualsVObject($expected, $output);
+        self::assertVObjectEqualsVObject($expected, $output);
     }
 
-    public function testSimple()
+    public function testSimple(): void
     {
         $blob = <<<ICS
 BEGIN:VCALENDAR
@@ -94,13 +93,13 @@ public function testSimple()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T120000Z/20110101T130000Z',
             $blob
         );
     }
 
-    public function testSource()
+    public function testSource(): void
     {
         $blob = <<<ICS
 BEGIN:VCALENDAR
@@ -115,7 +114,7 @@ public function testSource()
         fwrite($h, $blob);
         rewind($h);
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T120000Z/20110101T130000Z',
             $h
         );
@@ -124,7 +123,7 @@ public function testSource()
     /**
      * Testing TRANSP:OPAQUE.
      */
-    public function testOpaque()
+    public function testOpaque(): void
     {
         $blob = <<<ICS
 BEGIN:VCALENDAR
@@ -137,7 +136,7 @@ public function testOpaque()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T130000Z/20110101T140000Z',
             $blob
         );
@@ -146,7 +145,7 @@ public function testOpaque()
     /**
      * Testing TRANSP:TRANSPARENT.
      */
-    public function testTransparent()
+    public function testTransparent(): void
     {
         // transparent, hidden
         $blob = <<<ICS
@@ -160,7 +159,7 @@ public function testTransparent()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             '',
             $blob
         );
@@ -169,7 +168,7 @@ public function testTransparent()
     /**
      * Testing STATUS:CANCELLED.
      */
-    public function testCancelled()
+    public function testCancelled(): void
     {
         // transparent, hidden
         $blob = <<<ICS
@@ -183,7 +182,7 @@ public function testCancelled()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             '',
             $blob
         );
@@ -192,7 +191,7 @@ public function testCancelled()
     /**
      * Testing STATUS:TENTATIVE.
      */
-    public function testTentative()
+    public function testTentative(): void
     {
         // tentative, shows up
         $blob = <<<ICS
@@ -206,18 +205,18 @@ public function testTentative()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY;FBTYPE=BUSY-TENTATIVE:20110101T180000Z/20110101T190000Z',
             $blob
         );
     }
 
     /**
-     * Testing an event that falls outside of the report time-range.
+     * Testing an event that falls outside the report time-range.
      */
-    public function testOutsideTimeRange()
+    public function testOutsideTimeRange(): void
     {
-        // outside of time-range, hidden
+        // outside time-range, hidden
         $blob = <<<ICS
 BEGIN:VCALENDAR
 BEGIN:VEVENT
@@ -228,18 +227,18 @@ public function testOutsideTimeRange()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             '',
             $blob
         );
     }
 
     /**
-     * Testing an event that falls outside of the report time-range.
+     * Testing an event that falls outside the report time-range.
      */
-    public function testOutsideTimeRange2()
+    public function testOutsideTimeRange2(): void
     {
-        // outside of time-range, hidden
+        // outside time-range, hidden
         $blob = <<<ICS
 BEGIN:VCALENDAR
 BEGIN:VEVENT
@@ -250,7 +249,7 @@ public function testOutsideTimeRange2()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             '',
             $blob
         );
@@ -259,7 +258,7 @@ public function testOutsideTimeRange2()
     /**
      * Testing an event that uses DURATION.
      */
-    public function testDuration()
+    public function testDuration(): void
     {
         // using duration, shows up
         $blob = <<<ICS
@@ -272,7 +271,7 @@ public function testDuration()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T190000Z/20110101T200000Z',
             $blob
         );
@@ -281,7 +280,7 @@ public function testDuration()
     /**
      * Testing an all-day event.
      */
-    public function testAllDay()
+    public function testAllDay(): void
     {
         // Day-long event, shows up
         $blob = <<<ICS
@@ -293,7 +292,7 @@ public function testAllDay()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110102T000000Z/20110103T000000Z',
             $blob
         );
@@ -302,7 +301,7 @@ public function testAllDay()
     /**
      * Testing an event that has no end or duration.
      */
-    public function testNoDuration()
+    public function testNoDuration(): void
     {
         // No duration, does not show up
         $blob = <<<ICS
@@ -314,7 +313,7 @@ public function testNoDuration()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             '',
             $blob
         );
@@ -323,7 +322,7 @@ public function testNoDuration()
     /**
      * Testing feeding the freebusy generator an object instead of a string.
      */
-    public function testObject()
+    public function testObject(): void
     {
         // encoded as object, shows up
         $blob = <<<ICS
@@ -336,7 +335,7 @@ public function testObject()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T210000Z/20110101T220000Z',
             Reader::read($blob)
         );
@@ -345,7 +344,7 @@ public function testObject()
     /**
      * Testing feeding VFREEBUSY objects instead of VEVENT.
      */
-    public function testVFreeBusy()
+    public function testVFreeBusy(): void
     {
         // Freebusy. Some parts show up
         $blob = <<<ICS
@@ -360,14 +359,14 @@ public function testVFreeBusy()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             "FREEBUSY:20110103T010000Z/20110103T020000Z\n".
             'FREEBUSY:20110103T030000Z/20110103T060000Z',
             $blob
         );
     }
 
-    public function testYearlyRecurrence()
+    public function testYearlyRecurrence(): void
     {
         // Yearly recurrence rule, shows up
         $blob = <<<ICS
@@ -381,13 +380,13 @@ public function testYearlyRecurrence()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T220000Z/20110101T230000Z',
             $blob
         );
     }
 
-    public function testYearlyRecurrenceDuration()
+    public function testYearlyRecurrenceDuration(): void
     {
         // Yearly recurrence rule + duration, shows up
         $blob = <<<ICS
@@ -401,13 +400,13 @@ public function testYearlyRecurrenceDuration()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T230000Z/20110102T000000Z',
             $blob
         );
     }
 
-    public function testFloatingTime()
+    public function testFloatingTime(): void
     {
         // Floating time, no timezone
         $blob = <<<ICS
@@ -420,13 +419,13 @@ public function testFloatingTime()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T120000Z/20110101T130000Z',
             $blob
         );
     }
 
-    public function testFloatingTimeReferenceTimeZone()
+    public function testFloatingTimeReferenceTimeZone(): void
     {
         // Floating time + reference timezone
         $blob = <<<ICS
@@ -439,16 +438,16 @@ public function testFloatingTimeReferenceTimeZone()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T170000Z/20110101T180000Z',
             $blob,
             new \DateTimeZone('America/Toronto')
         );
     }
 
-    public function testAllDay2()
+    public function testAllDay2(): void
     {
-        // All-day event, slightly outside of the VFREEBUSY range.
+        // All-day event, slightly outside the VFREEBUSY range.
         $blob = <<<ICS
 BEGIN:VCALENDAR
 BEGIN:VEVENT
@@ -458,13 +457,13 @@ public function testAllDay2()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T110000Z/20110102T000000Z',
             $blob
         );
     }
 
-    public function testAllDayReferenceTimeZone()
+    public function testAllDayReferenceTimeZone(): void
     {
         // All-day event + reference timezone
         $blob = <<<ICS
@@ -476,14 +475,14 @@ public function testAllDayReferenceTimeZone()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T110000Z/20110102T050000Z',
             $blob,
             new \DateTimeZone('America/Toronto')
         );
     }
 
-    public function testNoValidInstances()
+    public function testNoValidInstances(): void
     {
         // Recurrence rule with no valid instances
         $blob = <<<ICS
@@ -498,7 +497,7 @@ public function testNoValidInstances()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             '',
             $blob
         );
@@ -508,7 +507,7 @@ public function testNoValidInstances()
      * This VAVAILABILITY object overlaps with the time-range, but we're just
      * busy the entire time.
      */
-    public function testVAvailabilitySimple()
+    public function testVAvailabilitySimple(): void
     {
         $blob = <<<ICS
 BEGIN:VCALENDAR
@@ -533,7 +532,7 @@ public function testVAvailabilitySimple()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             "FREEBUSY;FBTYPE=BUSY-UNAVAILABLE:20110101T110000Z/20110101T120000Z\n".
             "FREEBUSY:20110101T120000Z/20110101T130000Z\n".
             'FREEBUSY;FBTYPE=BUSY-UNAVAILABLE:20110101T130000Z/20110103T110000Z',
@@ -547,7 +546,7 @@ public function testVAvailabilitySimple()
      * This VAVAILABILITY object does not overlap at all with the freebusy
      * report, so it should be ignored.
      */
-    public function testVAvailabilityIrrelevant()
+    public function testVAvailabilityIrrelevant(): void
     {
         $blob = <<<ICS
 BEGIN:VCALENDAR
@@ -572,7 +571,7 @@ public function testVAvailabilityIrrelevant()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T120000Z/20110101T130000Z',
             $blob,
             null,
@@ -584,7 +583,7 @@ public function testVAvailabilityIrrelevant()
      * This VAVAILABILITY object has a 9am-5pm AVAILABLE object for office
      * hours.
      */
-    public function testVAvailabilityOfficeHours()
+    public function testVAvailabilityOfficeHours(): void
     {
         $blob = <<<ICS
 BEGIN:VCALENDAR
@@ -611,7 +610,7 @@ public function testVAvailabilityOfficeHours()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             "FREEBUSY;FBTYPE=BUSY-TENTATIVE:20110101T110000Z/20110101T120000Z\n".
             "FREEBUSY:20110101T120000Z/20110101T130000Z\n".
             "FREEBUSY;FBTYPE=BUSY-TENTATIVE:20110101T130000Z/20110103T090000Z\n",
@@ -625,7 +624,7 @@ public function testVAvailabilityOfficeHours()
      * This test has the same office hours, but has a vacation blocked off for
      * the relevant time, using a higher priority. (lower number).
      */
-    public function testVAvailabilityOfficeHoursVacation()
+    public function testVAvailabilityOfficeHoursVacation(): void
     {
         $blob = <<<ICS
 BEGIN:VCALENDAR
@@ -659,7 +658,7 @@ public function testVAvailabilityOfficeHoursVacation()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             'FREEBUSY:20110101T110000Z/20110103T110000Z',
             $blob,
             null,
@@ -673,7 +672,7 @@ public function testVAvailabilityOfficeHoursVacation()
      *
      * The end-result is that the vacation VAVAILABILITY is completely ignored.
      */
-    public function testVAvailabilityOfficeHoursVacation2()
+    public function testVAvailabilityOfficeHoursVacation2(): void
     {
         $blob = <<<ICS
 BEGIN:VCALENDAR
@@ -707,7 +706,7 @@ public function testVAvailabilityOfficeHoursVacation2()
 END:VCALENDAR
 ICS;
 
-        $this->assertFreeBusyReport(
+        self::assertFreeBusyReport(
             "FREEBUSY;FBTYPE=BUSY-TENTATIVE:20110101T110000Z/20110101T120000Z\n".
             "FREEBUSY:20110101T120000Z/20110101T130000Z\n".
             "FREEBUSY;FBTYPE=BUSY-TENTATIVE:20110101T130000Z/20110103T090000Z\n",
diff --git a/tests/VObject/GoogleColonEscapingTest.php b/tests/VObject/GoogleColonEscapingTest.php
index 48bbde07b..fa2ba8a7f 100644
--- a/tests/VObject/GoogleColonEscapingTest.php
+++ b/tests/VObject/GoogleColonEscapingTest.php
@@ -12,7 +12,7 @@
  */
 class GoogleColonEscapingTest extends TestCase
 {
-    public function testDecode()
+    public function testDecode(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -26,6 +26,6 @@ public function testDecode()
 VCF;
 
         $vobj = Reader::read($vcard);
-        $this->assertEquals('http://www.rooftopsolutions.nl/', $vobj->URL->getValue());
+        self::assertEquals('http://www.rooftopsolutions.nl/', $vobj->URL->getValue());
     }
 }
diff --git a/tests/VObject/ICalendar/AttachParseTest.php b/tests/VObject/ICalendar/AttachParseTest.php
index e6e3d8685..cb54eb341 100644
--- a/tests/VObject/ICalendar/AttachParseTest.php
+++ b/tests/VObject/ICalendar/AttachParseTest.php
@@ -11,7 +11,7 @@ class AttachParseTest extends TestCase
     /**
      * See issue #128 for more info.
      */
-    public function testParseAttach()
+    public function testParseAttach(): void
     {
         $vcal = <<<ICS
 BEGIN:VCALENDAR
@@ -24,7 +24,7 @@ public function testParseAttach()
         $vcal = Reader::read($vcal);
         $prop = $vcal->VEVENT->ATTACH;
 
-        $this->assertInstanceOf(Uri::class, $prop);
-        $this->assertEquals('ftp://example.com/pub/reports/r-960812.ps', $prop->getValue());
+        self::assertInstanceOf(Uri::class, $prop);
+        self::assertEquals('ftp://example.com/pub/reports/r-960812.ps', $prop->getValue());
     }
 }
diff --git a/tests/VObject/ITip/BrokerAttendeeReplyTest.php b/tests/VObject/ITip/BrokerAttendeeReplyTest.php
index 284075adf..98942af41 100644
--- a/tests/VObject/ITip/BrokerAttendeeReplyTest.php
+++ b/tests/VObject/ITip/BrokerAttendeeReplyTest.php
@@ -4,7 +4,7 @@
 
 class BrokerAttendeeReplyTest extends BrokerTester
 {
-    public function testAccepted()
+    public function testAccepted(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -68,7 +68,7 @@ public function testAccepted()
         $this->parse($oldMessage, $newMessage, $expected);
     }
 
-    public function testAcceptedWithTz()
+    public function testAcceptedWithTz(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -186,7 +186,7 @@ public function testAcceptedWithTz()
         $this->parse($oldMessage, $newMessage, $expected);
     }
 
-    public function testRecurringReply()
+    public function testRecurringReply(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -332,7 +332,7 @@ public function testRecurringReply()
         $this->parse($oldMessage, $newMessage, $expected);
     }
 
-    public function testRecurringAllDay()
+    public function testRecurringAllDay(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -471,7 +471,7 @@ public function testRecurringAllDay()
         $this->parse($oldMessage, $newMessage, $expected);
     }
 
-    public function testNoChange()
+    public function testNoChange(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -503,7 +503,7 @@ public function testNoChange()
         $this->parse($oldMessage, $newMessage, $expected);
     }
 
-    public function testNoChangeForceSend()
+    public function testNoChangeForceSend(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -562,7 +562,7 @@ public function testNoChangeForceSend()
         $this->parse($oldMessage, $newMessage, $expected);
     }
 
-    public function testNoRelevantAttendee()
+    public function testNoRelevantAttendee(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -602,7 +602,7 @@ public function testNoRelevantAttendee()
      * This should automatically generate a DECLINED message for that
      * specific instance.
      */
-    public function testCreateReplyByException()
+    public function testCreateReplyByException(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -671,7 +671,7 @@ public function testCreateReplyByException()
      *
      * @depends testCreateReplyByException
      */
-    public function testCreateReplyByExceptionTz()
+    public function testCreateReplyByExceptionTz(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -737,7 +737,7 @@ public function testCreateReplyByExceptionTz()
     /**
      * @depends testCreateReplyByException
      */
-    public function testCreateReplyByExceptionAllDay()
+    public function testCreateReplyByExceptionAllDay(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -803,7 +803,7 @@ public function testCreateReplyByExceptionAllDay()
         $this->parse($oldMessage, $newMessage, $expected);
     }
 
-    public function testDeclined()
+    public function testDeclined(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -864,7 +864,7 @@ public function testDeclined()
         $this->parse($oldMessage, $newMessage, $expected);
     }
 
-    public function testDeclinedCancelledEvent()
+    public function testDeclinedCancelledEvent(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -894,8 +894,6 @@ public function testDeclinedCancelledEvent()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
-
         $expected = [];
 
         $this->parse($oldMessage, $newMessage, $expected);
@@ -910,7 +908,7 @@ public function testDeclinedCancelledEvent()
      * For any other attendance status, the new status would have been
      * declined, but for this, no message should we sent.
      */
-    public function testDontCreateReplyWhenEventWasDeclined()
+    public function testDontCreateReplyWhenEventWasDeclined(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -955,7 +953,7 @@ public function testDontCreateReplyWhenEventWasDeclined()
         $this->parse($oldMessage, $newMessage, $expected);
     }
 
-    public function testScheduleAgentOnOrganizer()
+    public function testScheduleAgentOnOrganizer(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -983,13 +981,11 @@ public function testScheduleAgentOnOrganizer()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
-
         $expected = [];
         $this->parse($oldMessage, $newMessage, $expected);
     }
 
-    public function testAcceptedAllDay()
+    public function testAcceptedAllDay(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -1057,7 +1053,7 @@ public function testAcceptedAllDay()
      * This is possible in cases an organizer created a recurring event, and
      * invited an attendee for one instance of the event.
      */
-    public function testReplyNoMasterEvent()
+    public function testReplyNoMasterEvent(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -1089,8 +1085,6 @@ public function testReplyNoMasterEvent()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
-
         $expected = [
             [
                 'uid' => 'foobar',
@@ -1129,7 +1123,7 @@ public function testReplyNoMasterEvent()
      *
      * @depends testAccepted
      */
-    public function testPartyCrasher()
+    public function testPartyCrasher(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
diff --git a/tests/VObject/ITip/BrokerDeleteEventTest.php b/tests/VObject/ITip/BrokerDeleteEventTest.php
index 88f30ec18..4de219f82 100644
--- a/tests/VObject/ITip/BrokerDeleteEventTest.php
+++ b/tests/VObject/ITip/BrokerDeleteEventTest.php
@@ -4,7 +4,7 @@
 
 class BrokerDeleteEventTest extends BrokerTester
 {
-    public function testOrganizerDeleteWithDtend()
+    public function testOrganizerDeleteWithDtend(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -87,7 +87,7 @@ public function testOrganizerDeleteWithDtend()
         $this->parse($oldMessage, $newMessage, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testOrganizerDeleteWithDuration()
+    public function testOrganizerDeleteWithDuration(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -170,7 +170,7 @@ public function testOrganizerDeleteWithDuration()
         $this->parse($oldMessage, $newMessage, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testAttendeeDeleteWithDtend()
+    public function testAttendeeDeleteWithDtend(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -225,7 +225,7 @@ public function testAttendeeDeleteWithDtend()
         $this->parse($oldMessage, $newMessage, $expected, 'mailto:one@example.org');
     }
 
-    public function testAttendeeReplyWithDuration()
+    public function testAttendeeReplyWithDuration(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -280,7 +280,7 @@ public function testAttendeeReplyWithDuration()
         $this->parse($oldMessage, $newMessage, $expected, 'mailto:one@example.org');
     }
 
-    public function testAttendeeDeleteCancelledEvent()
+    public function testAttendeeDeleteCancelledEvent(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -305,12 +305,12 @@ public function testAttendeeDeleteCancelledEvent()
         $this->parse($oldMessage, $newMessage, $expected, 'mailto:one@example.org');
     }
 
-    public function testNoCalendar()
+    public function testNoCalendar(): void
     {
         $this->parse(null, null, [], 'mailto:one@example.org');
     }
 
-    public function testVTodo()
+    public function testVTodo(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
diff --git a/tests/VObject/ITip/BrokerNewEventTest.php b/tests/VObject/ITip/BrokerNewEventTest.php
index f5b89b0e8..d85455295 100644
--- a/tests/VObject/ITip/BrokerNewEventTest.php
+++ b/tests/VObject/ITip/BrokerNewEventTest.php
@@ -2,9 +2,11 @@
 
 namespace Sabre\VObject\ITip;
 
+use Sabre\VObject\Version;
+
 class BrokerNewEventTest extends BrokerTester
 {
-    public function testNoAttendee()
+    public function testNoAttendee(): void
     {
         $message = <<<ICS
 BEGIN:VCALENDAR
@@ -16,10 +18,10 @@ public function testNoAttendee()
 END:VCALENDAR
 ICS;
 
-        $result = $this->parse(null, $message, []);
+        $this->parse(null, $message, []);
     }
 
-    public function testVTODO()
+    public function testVTODO(): void
     {
         $message = <<<ICS
 BEGIN:VCALENDAR
@@ -29,10 +31,10 @@ public function testVTODO()
 END:VCALENDAR
 ICS;
 
-        $result = $this->parse(null, $message, []);
+        $this->parse(null, $message, []);
     }
 
-    public function testSimpleInvite()
+    public function testSimpleInvite(): void
     {
         $message = <<<ICS
 BEGIN:VCALENDAR
@@ -47,7 +49,7 @@ public function testSimpleInvite()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
         $expectedMessage = <<<ICS
 BEGIN:VCALENDAR
 VERSION:2.0
@@ -81,7 +83,7 @@ public function testSimpleInvite()
         $this->parse(null, $message, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testBrokenEventUIDMisMatch()
+    public function testBrokenEventUIDMisMatch(): void
     {
         $this->expectException(ITipException::class);
         $message = <<<ICS
@@ -103,7 +105,7 @@ public function testBrokenEventUIDMisMatch()
         $this->parse(null, $message, [], 'mailto:strunk@example.org');
     }
 
-    public function testBrokenEventOrganizerMisMatch()
+    public function testBrokenEventOrganizerMisMatch(): void
     {
         $this->expectException(ITipException::class);
         $message = <<<ICS
@@ -125,7 +127,7 @@ public function testBrokenEventOrganizerMisMatch()
         $this->parse(null, $message, [], 'mailto:strunk@example.org');
     }
 
-    public function testRecurrenceInvite()
+    public function testRecurrenceInvite(): void
     {
         $message = <<<ICS
 BEGIN:VCALENDAR
@@ -152,7 +154,7 @@ public function testRecurrenceInvite()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $expected = [
             [
@@ -253,7 +255,7 @@ public function testRecurrenceInvite()
         $this->parse(null, $message, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testRecurrenceInvite2()
+    public function testRecurrenceInvite2(): void
     {
         // This method tests a nearly identical path, but in this case the
         // master event does not have an EXDATE.
@@ -281,7 +283,7 @@ public function testRecurrenceInvite2()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $expected = [
             [
@@ -381,7 +383,7 @@ public function testRecurrenceInvite2()
         $this->parse(null, $message, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testRecurrenceInvite3()
+    public function testRecurrenceInvite3(): void
     {
         // This method tests a complex rrule
         $message = <<<ICS
@@ -398,7 +400,7 @@ public function testRecurrenceInvite3()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $expected = [
             [
@@ -432,7 +434,7 @@ public function testRecurrenceInvite3()
         $this->parse(null, $message, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testScheduleAgentClient()
+    public function testScheduleAgentClient(): void
     {
         $message = <<<ICS
 BEGIN:VCALENDAR
@@ -447,12 +449,10 @@ public function testScheduleAgentClient()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
-
         $this->parse(null, $message, [], 'mailto:strunk@example.org');
     }
 
-    public function testMultipleUID()
+    public function testMultipleUID(): void
     {
         $this->expectException(ITipException::class);
         $message = <<<ICS
@@ -479,11 +479,10 @@ public function testMultipleUID()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
         $this->parse(null, $message, [], 'mailto:strunk@example.org');
     }
 
-    public function testChangingOrganizers()
+    public function testChangingOrganizers(): void
     {
         $this->expectException(SameOrganizerForAllComponentsException::class);
         $message = <<<ICS
@@ -513,7 +512,7 @@ public function testChangingOrganizers()
         $this->parse(null, $message, [], 'mailto:strunk@example.org');
     }
 
-    public function testCaseInsensitiveOrganizers()
+    public function testCaseInsensitiveOrganizers(): void
     {
         $message = <<<ICS
 BEGIN:VCALENDAR
@@ -560,7 +559,7 @@ public function testCaseInsensitiveOrganizers()
         ], 'mailto:strunk@example.org');
     }
 
-    public function testNoOrganizerHasAttendee()
+    public function testNoOrganizerHasAttendee(): void
     {
         $message = <<<ICS
 BEGIN:VCALENDAR
diff --git a/tests/VObject/ITip/BrokerProcessMessageTest.php b/tests/VObject/ITip/BrokerProcessMessageTest.php
index 3327be0d9..8f5a0523d 100644
--- a/tests/VObject/ITip/BrokerProcessMessageTest.php
+++ b/tests/VObject/ITip/BrokerProcessMessageTest.php
@@ -4,7 +4,7 @@
 
 class BrokerProcessMessageTest extends BrokerTester
 {
-    public function testRequestNew()
+    public function testRequestNew(): void
     {
         $itip = <<<ICS
 BEGIN:VCALENDAR
@@ -27,10 +27,10 @@ public function testRequestNew()
 END:VCALENDAR
 ICS;
 
-        $result = $this->process($itip, null, $expected);
+        $this->process($itip, null, $expected);
     }
 
-    public function testRequestUpdate()
+    public function testRequestUpdate(): void
     {
         $itip = <<<ICS
 BEGIN:VCALENDAR
@@ -61,10 +61,10 @@ public function testRequestUpdate()
 END:VCALENDAR
 ICS;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testCancel()
+    public function testCancel(): void
     {
         $itip = <<<ICS
 BEGIN:VCALENDAR
@@ -96,10 +96,10 @@ public function testCancel()
 END:VCALENDAR
 ICS;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testCancelNoExistingEvent()
+    public function testCancelNoExistingEvent(): void
     {
         $itip = <<<ICS
 BEGIN:VCALENDAR
@@ -115,10 +115,10 @@ public function testCancelNoExistingEvent()
         $old = null;
         $expected = null;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testUnsupportedComponent()
+    public function testUnsupportedComponent(): void
     {
         $itip = <<<ICS
 BEGIN:VCALENDAR
@@ -133,10 +133,10 @@ public function testUnsupportedComponent()
         $old = null;
         $expected = null;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testUnsupportedMethod()
+    public function testUnsupportedMethod(): void
     {
         $itip = <<<ICS
 BEGIN:VCALENDAR
@@ -152,6 +152,6 @@ public function testUnsupportedMethod()
         $old = null;
         $expected = null;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 }
diff --git a/tests/VObject/ITip/BrokerProcessReplyTest.php b/tests/VObject/ITip/BrokerProcessReplyTest.php
index bbfd6c419..064d5cb48 100644
--- a/tests/VObject/ITip/BrokerProcessReplyTest.php
+++ b/tests/VObject/ITip/BrokerProcessReplyTest.php
@@ -4,7 +4,7 @@
 
 class BrokerProcessReplyTest extends BrokerTester
 {
-    public function testReplyNoOriginal()
+    public function testReplyNoOriginal(): void
     {
         $itip = <<<ICS
 BEGIN:VCALENDAR
@@ -22,10 +22,10 @@ public function testReplyNoOriginal()
         $old = null;
         $expected = null;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testReplyAccept()
+    public function testReplyAccept(): void
     {
         $itip = <<<ICS
 BEGIN:VCALENDAR
@@ -64,10 +64,10 @@ public function testReplyAccept()
 END:VCALENDAR
 ICS;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testReplyWithTz()
+    public function testReplyWithTz(): void
     {
         $itip = <<<ICS
 BEGIN:VCALENDAR
@@ -163,10 +163,10 @@ public function testReplyWithTz()
 END:VCALENDAR
 ICS;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testReplyRequestStatus()
+    public function testReplyRequestStatus(): void
     {
         $itip = <<<ICS
 BEGIN:VCALENDAR
@@ -207,10 +207,10 @@ public function testReplyRequestStatus()
 END:VCALENDAR
 ICS;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testReplyPartyCrasher()
+    public function testReplyPartyCrasher(): void
     {
         $itip = <<<ICS
 BEGIN:VCALENDAR
@@ -250,10 +250,10 @@ public function testReplyPartyCrasher()
 END:VCALENDAR
 ICS;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testReplyNewException()
+    public function testReplyNewException(): void
     {
         // This is a reply to 1 instance of a recurring event. This should
         // automatically create an exception.
@@ -310,10 +310,10 @@ public function testReplyNewException()
 END:VCALENDAR
 ICS;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testReplyNewExceptionTz()
+    public function testReplyNewExceptionTz(): void
     {
         // This is a reply to 1 instance of a recurring event. This should
         // automatically create an exception.
@@ -370,10 +370,10 @@ public function testReplyNewExceptionTz()
 END:VCALENDAR
 ICS;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testReplyPartyCrashCreateException()
+    public function testReplyPartyCrashCreateException(): void
     {
         // IN this test there's a recurring event that has an exception. The
         // exception is missing the attendee.
@@ -431,10 +431,10 @@ public function testReplyPartyCrashCreateException()
 END:VCALENDAR
 ICS;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testReplyNewExceptionNoMasterEvent()
+    public function testReplyNewExceptionNoMasterEvent(): void
     {
         /**
          * This iTip message would normally create a new exception, but the
@@ -473,13 +473,13 @@ public function testReplyNewExceptionNoMasterEvent()
 ICS;
 
         $expected = null;
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
     /**
      * @depends testReplyAccept
      */
-    public function testReplyAcceptUpdateRSVP()
+    public function testReplyAcceptUpdateRSVP(): void
     {
         $itip = <<<ICS
 BEGIN:VCALENDAR
@@ -518,10 +518,10 @@ public function testReplyAcceptUpdateRSVP()
 END:VCALENDAR
 ICS;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 
-    public function testReplyNewExceptionFirstOccurence()
+    public function testReplyNewExceptionFirstOccurrence(): void
     {
         // This is a reply to 1 instance of a recurring event. This should
         // automatically create an exception.
@@ -578,6 +578,6 @@ public function testReplyNewExceptionFirstOccurence()
 END:VCALENDAR
 ICS;
 
-        $result = $this->process($itip, $old, $expected);
+        $this->process($itip, $old, $expected);
     }
 }
diff --git a/tests/VObject/ITip/BrokerSignificantChangesTest.php b/tests/VObject/ITip/BrokerSignificantChangesTest.php
index a20d55025..44843615e 100644
--- a/tests/VObject/ITip/BrokerSignificantChangesTest.php
+++ b/tests/VObject/ITip/BrokerSignificantChangesTest.php
@@ -7,7 +7,7 @@ class BrokerSignificantChangesTest extends BrokerTester
     /**
      * Check significant changes detection (no change).
      */
-    public function testSignificantChangesNoChange()
+    public function testSignificantChangesNoChange(): void
     {
         $old = <<<ICS
 BEGIN:VCALENDAR
@@ -41,7 +41,7 @@ public function testSignificantChangesNoChange()
     /**
      * Check significant changes detection (no change).
      */
-    public function testSignificantChangesRRuleNoChange()
+    public function testSignificantChangesRRuleNoChange(): void
     {
         $old = <<<ICS
 BEGIN:VCALENDAR
@@ -75,7 +75,7 @@ public function testSignificantChangesRRuleNoChange()
     /**
      * Check significant changes detection (no change).
      */
-    public function testSignificantChangesRRuleOrderNoChange()
+    public function testSignificantChangesRRuleOrderNoChange(): void
     {
         $old = <<<ICS
 BEGIN:VCALENDAR
@@ -111,7 +111,7 @@ public function testSignificantChangesRRuleOrderNoChange()
      * Reordering of the attendees should not be a significant change (#540)
      * https://github.com/sabre-io/vobject/issues/540.
      */
-    public function testSignificantChangesAttendeesOrderNoChange()
+    public function testSignificantChangesAttendeesOrderNoChange(): void
     {
         $old = <<<ICS
 BEGIN:VCALENDAR
@@ -154,7 +154,7 @@ public function testSignificantChangesAttendeesOrderNoChange()
      * not be a significant change
      * https://github.com/sabre-io/vobject/issues/542.
      */
-    public function testSignificantChangesVeventOrderNoChange()
+    public function testSignificantChangesVeventOrderNoChange(): void
     {
         $vevent1 = <<<ICS
 BEGIN:VEVENT
diff --git a/tests/VObject/ITip/BrokerTester.php b/tests/VObject/ITip/BrokerTester.php
index 9e9956e03..cc01ed3f9 100644
--- a/tests/VObject/ITip/BrokerTester.php
+++ b/tests/VObject/ITip/BrokerTester.php
@@ -3,7 +3,14 @@
 namespace Sabre\VObject\ITip;
 
 use PHPUnit\Framework\TestCase;
+use Sabre\VObject\Component\VEvent;
+use Sabre\VObject\InvalidDataException;
+use Sabre\VObject\ParseException;
+use Sabre\VObject\PHPUnitAssertions;
 use Sabre\VObject\Reader;
+use Sabre\VObject\Recur\MaxInstancesExceededException;
+use Sabre\VObject\Recur\NoInstancesException;
+use Sabre\VObject\Version;
 
 /**
  * Utilities for testing the broker.
@@ -14,38 +21,44 @@
  */
 abstract class BrokerTester extends TestCase
 {
-    use \Sabre\VObject\PHPUnitAssertions;
+    use PHPUnitAssertions;
 
-    public function parse($oldMessage, $newMessage, $expected = [], $currentUser = 'mailto:one@example.org')
+    public function parse($oldMessage, $newMessage, array $expected = [], string $currentUser = 'mailto:one@example.org'): void
     {
         $broker = new Broker();
         $result = $broker->parseEvent($newMessage, $currentUser, $oldMessage);
 
-        $this->assertEquals(count($expected), count($result));
+        self::assertSameSize($expected, $result);
 
         foreach ($expected as $index => $ex) {
             $message = $result[$index];
 
             foreach ($ex as $key => $val) {
                 if ('message' === $key) {
-                    $this->assertVObjectEqualsVObject(
+                    self::assertVObjectEqualsVObject(
                         $val,
                         $message->message->serialize()
                     );
                 } else {
-                    $this->assertEquals($val, $message->$key);
+                    self::assertEquals($val, $message->$key);
                 }
             }
         }
     }
 
-    public function process($input, $existingObject = null, $expected = false)
+    /**
+     * @throws ParseException
+     * @throws MaxInstancesExceededException
+     * @throws NoInstancesException
+     * @throws InvalidDataException
+     */
+    public function process($input, $existingObject = null, $expected = false): void
     {
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $vcal = Reader::read($input);
 
-        $mainComponent = new \Sabre\VObject\Component\VEvent($vcal, 'VEVENT');
+        $mainComponent = new VEvent($vcal, 'VEVENT');
         foreach ($vcal->getComponents() as $mainComponent) {
             if ('VEVENT' === $mainComponent->name) {
                 break;
@@ -80,12 +93,12 @@ public function process($input, $existingObject = null, $expected = false)
         $result = $broker->processMessage($message, $existingObject);
 
         if (is_null($expected)) {
-            $this->assertTrue(!$result);
+            self::assertTrue(!$result);
 
             return;
         }
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $result
         );
diff --git a/tests/VObject/ITip/BrokerTimezoneInParseEventInfoWithoutMasterTest.php b/tests/VObject/ITip/BrokerTimezoneInParseEventInfoWithoutMasterTest.php
index 1635be742..e3f18f15e 100644
--- a/tests/VObject/ITip/BrokerTimezoneInParseEventInfoWithoutMasterTest.php
+++ b/tests/VObject/ITip/BrokerTimezoneInParseEventInfoWithoutMasterTest.php
@@ -7,7 +7,7 @@
 
 class BrokerTimezoneInParseEventInfoWithoutMasterTest extends TestCase
 {
-    public function testTimezoneInParseEventInfoWithoutMaster()
+    public function testTimezoneInParseEventInfoWithoutMaster(): void
     {
         $calendar = <<<ICS
 BEGIN:VCALENDAR
@@ -72,7 +72,7 @@ public function testTimezoneInParseEventInfoWithoutMaster()
         $reflectionMethod = new \ReflectionMethod($broker, 'parseEventInfo');
         $reflectionMethod->setAccessible(true);
         $data = $reflectionMethod->invoke($broker, $calendar);
-        $this->assertInstanceOf('DateTimeZone', $data['timezone']);
-        $this->assertEquals($data['timezone']->getName(), 'Europe/Minsk');
+        self::assertInstanceOf('DateTimeZone', $data['timezone']);
+        self::assertEquals('Europe/Minsk', $data['timezone']->getName());
     }
 }
diff --git a/tests/VObject/ITip/BrokerUpdateEventTest.php b/tests/VObject/ITip/BrokerUpdateEventTest.php
index e93f89652..1497bb711 100644
--- a/tests/VObject/ITip/BrokerUpdateEventTest.php
+++ b/tests/VObject/ITip/BrokerUpdateEventTest.php
@@ -2,9 +2,11 @@
 
 namespace Sabre\VObject\ITip;
 
+use Sabre\VObject\Version;
+
 class BrokerUpdateEventTest extends BrokerTester
 {
-    public function testInviteChange()
+    public function testInviteChange(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -40,7 +42,7 @@ public function testInviteChange()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $expected = [
             [
@@ -136,7 +138,7 @@ public function testInviteChange()
         $this->parse($oldMessage, $newMessage, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testInviteChangeFromNonSchedulingToSchedulingObject()
+    public function testInviteChangeFromNonSchedulingToSchedulingObject(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -164,7 +166,7 @@ public function testInviteChangeFromNonSchedulingToSchedulingObject()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $expected = [
             [
@@ -198,7 +200,7 @@ public function testInviteChangeFromNonSchedulingToSchedulingObject()
         $this->parse($oldMessage, $newMessage, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testInviteChangeFromSchedulingToNonSchedulingObject()
+    public function testInviteChangeFromSchedulingToNonSchedulingObject(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -226,7 +228,7 @@ public function testInviteChangeFromSchedulingToNonSchedulingObject()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $expected = [
             [
@@ -256,7 +258,7 @@ public function testInviteChangeFromSchedulingToNonSchedulingObject()
         $this->parse($oldMessage, $newMessage, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testNoAttendees()
+    public function testNoAttendees(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -282,13 +284,11 @@ public function testNoAttendees()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
-
         $expected = [];
         $this->parse($oldMessage, $newMessage, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testRemoveInstance()
+    public function testRemoveInstance(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -321,7 +321,7 @@ public function testRemoveInstance()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $expected = [
             [
@@ -363,7 +363,7 @@ public function testRemoveInstance()
      *
      * This should ensure that the message is significant for every attendee,
      */
-    public function testInviteChangeSignificantChange()
+    public function testInviteChangeSignificantChange(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -399,7 +399,7 @@ public function testInviteChangeSignificantChange()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $expected = [
             [
@@ -494,7 +494,7 @@ public function testInviteChangeSignificantChange()
         $this->parse($oldMessage, $newMessage, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testInviteNoChange()
+    public function testInviteNoChange(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -526,7 +526,7 @@ public function testInviteNoChange()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $expected = [
             [
@@ -562,7 +562,7 @@ public function testInviteNoChange()
         $this->parse($oldMessage, $newMessage, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testInviteNoChangeForceSend()
+    public function testInviteNoChangeForceSend(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -594,7 +594,7 @@ public function testInviteNoChangeForceSend()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $expected = [
             [
@@ -630,7 +630,7 @@ public function testInviteNoChangeForceSend()
         $this->parse($oldMessage, $newMessage, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testInviteRemoveAttendees()
+    public function testInviteRemoveAttendees(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -662,7 +662,7 @@ public function testInviteRemoveAttendees()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $expected = [
             [
@@ -723,10 +723,10 @@ public function testInviteRemoveAttendees()
             ],
         ];
 
-        $result = $this->parse($oldMessage, $newMessage, $expected, 'mailto:strunk@example.org');
+        $this->parse($oldMessage, $newMessage, $expected, 'mailto:strunk@example.org');
     }
 
-    public function testInviteChangeExdateOrder()
+    public function testInviteChangeExdateOrder(): void
     {
         $oldMessage = <<<ICS
 BEGIN:VCALENDAR
@@ -774,7 +774,7 @@ public function testInviteChangeExdateOrder()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
 
         $expected = [
             [
diff --git a/tests/VObject/ITip/EvolutionTest.php b/tests/VObject/ITip/EvolutionTest.php
index 686a94db1..02ed4dc19 100644
--- a/tests/VObject/ITip/EvolutionTest.php
+++ b/tests/VObject/ITip/EvolutionTest.php
@@ -2,14 +2,16 @@
 
 namespace Sabre\VObject\ITip;
 
+use Sabre\VObject\Version;
+
 class EvolutionTest extends BrokerTester
 {
     /**
-     * Evolution does things as usual a little bit differently.
+     * Evolution does things as usual a little differently.
      *
      * We're adding a separate test just for it.
      */
-    public function testNewEvolutionEvent()
+    public function testNewEvolutionEvent(): void
     {
         $ics = <<<ICS
 BEGIN:VCALENDAR
@@ -865,7 +867,7 @@ public function testNewEvolutionEvent()
 END:VCALENDAR
 ICS;
 
-        $version = \Sabre\VObject\Version::VERSION;
+        $version = Version::VERSION;
         $expectedICS = <<<ICS
 BEGIN:VCALENDAR
 VERSION:2.0
@@ -1741,7 +1743,7 @@ public function testNewEvolutionEvent()
      * again mangled by iCal. This triggered a few bugs related to email
      * address scheme casing.
      */
-    public function testAttendeeModify()
+    public function testAttendeeModify(): void
     {
         $old = <<<ICS
 BEGIN:VCALENDAR
diff --git a/tests/VObject/ITip/MessageTest.php b/tests/VObject/ITip/MessageTest.php
index 56fcf8274..3196c1aa4 100644
--- a/tests/VObject/ITip/MessageTest.php
+++ b/tests/VObject/ITip/MessageTest.php
@@ -6,25 +6,25 @@
 
 class MessageTest extends TestCase
 {
-    public function testNoScheduleStatus()
+    public function testNoScheduleStatus(): void
     {
         $message = new Message();
-        $this->assertFalse($message->getScheduleStatus());
+        self::assertFalse($message->getScheduleStatus());
     }
 
-    public function testScheduleStatus()
+    public function testScheduleStatus(): void
     {
         $message = new Message();
         $message->scheduleStatus = '1.2;Delivered';
 
-        $this->assertEquals('1.2', $message->getScheduleStatus());
+        self::assertEquals('1.2', $message->getScheduleStatus());
     }
 
-    public function testUnexpectedScheduleStatus()
+    public function testUnexpectedScheduleStatus(): void
     {
         $message = new Message();
         $message->scheduleStatus = '9.9.9';
 
-        $this->assertEquals('9.9.9', $message->getScheduleStatus());
+        self::assertEquals('9.9.9', $message->getScheduleStatus());
     }
 }
diff --git a/tests/VObject/Issue153Test.php b/tests/VObject/Issue153Test.php
index 309025041..83e56cf50 100644
--- a/tests/VObject/Issue153Test.php
+++ b/tests/VObject/Issue153Test.php
@@ -6,9 +6,9 @@
 
 class Issue153Test extends TestCase
 {
-    public function testRead()
+    public function testRead(): void
     {
         $obj = Reader::read(file_get_contents(dirname(__FILE__).'/issue153.vcf'));
-        $this->assertEquals('Test Benutzer', (string) $obj->FN);
+        self::assertEquals('Test Benutzer', (string) $obj->FN);
     }
 }
diff --git a/tests/VObject/Issue259Test.php b/tests/VObject/Issue259Test.php
index 3227fcd56..5c014ad3c 100644
--- a/tests/VObject/Issue259Test.php
+++ b/tests/VObject/Issue259Test.php
@@ -6,7 +6,7 @@
 
 class Issue259Test extends TestCase
 {
-    public function testParsingJcalWithUntil()
+    public function testParsingJcalWithUntil(): void
     {
         $jcalWithUntil = '["vcalendar",[],[["vevent",[["uid",{},"text","dd1f7d29"],["organizer",{"cn":"robert"},"cal-address","mailto:robert@robert.com"],["dtstart",{"tzid":"Europe/Berlin"},"date-time","2015-10-21T12:00:00"],["dtend",{"tzid":"Europe/Berlin"},"date-time","2015-10-21T13:00:00"],["transp",{},"text","OPAQUE"],["rrule",{},"recur",{"freq":"MONTHLY","until":"2016-01-01T22:00:00Z"}]],[]]]]';
         $parser = new Parser\Json();
@@ -17,7 +17,7 @@ public function testParsingJcalWithUntil()
         $event = reset($eventAsArray);
         $rruleAsArray = $event->select('RRULE');
         $rrule = reset($rruleAsArray);
-        $this->assertNotNull($rrule);
-        $this->assertEquals($rrule->getValue(), 'FREQ=MONTHLY;UNTIL=20160101T220000Z');
+        self::assertNotNull($rrule);
+        self::assertEquals('FREQ=MONTHLY;UNTIL=20160101T220000Z', $rrule->getValue());
     }
 }
diff --git a/tests/VObject/Issue36WorkAroundTest.php b/tests/VObject/Issue36WorkAroundTest.php
index 1afd3d184..e6c4f254e 100644
--- a/tests/VObject/Issue36WorkAroundTest.php
+++ b/tests/VObject/Issue36WorkAroundTest.php
@@ -6,7 +6,7 @@
 
 class Issue36WorkAroundTest extends TestCase
 {
-    public function testWorkaround()
+    public function testWorkaround(): void
     {
         // See https://github.com/fruux/sabre-vobject/issues/36
         $event = <<<ICS
@@ -34,6 +34,6 @@ public function testWorkaround()
 
         // If this does not throw an exception, it's all good.
         $it = new Recur\EventIterator($obj, '1833bd44-188b-405c-9f85-1a12105318aa');
-        $this->assertInstanceOf(Recur\EventIterator::class, $it);
+        self::assertInstanceOf(Recur\EventIterator::class, $it);
     }
 }
diff --git a/tests/VObject/Issue40Test.php b/tests/VObject/Issue40Test.php
index 1cf9986e9..3d280ed4d 100644
--- a/tests/VObject/Issue40Test.php
+++ b/tests/VObject/Issue40Test.php
@@ -11,7 +11,7 @@
  */
 class Issue40Test extends TestCase
 {
-    public function testEncode()
+    public function testEncode(): void
     {
         $card = new Component\VCard();
         $card->add('N', ['van der Harten', ['Rene', 'J.'], '', 'Sir', 'R.D.O.N.'], ['SORT-AS' => ['Harten', 'Rene']]);
@@ -27,6 +27,6 @@ public function testEncode()
             '',
         ]);
 
-        $this->assertEquals($expected, $card->serialize());
+        self::assertEquals($expected, $card->serialize());
     }
 }
diff --git a/tests/VObject/Issue467Test.php b/tests/VObject/Issue467Test.php
new file mode 100644
index 000000000..27f1b49bc
--- /dev/null
+++ b/tests/VObject/Issue467Test.php
@@ -0,0 +1,56 @@
+<?php
+
+namespace Sabre\VObject;
+
+use PHPUnit\Framework\TestCase;
+
+class Issue467Test extends TestCase
+{
+    public function testRead(): void
+    {
+        $data = 'BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Sabre//Sabre VObject 4.3.5//EN
+CALSCALE:GREGORIAN
+BEGIN:VTIMEZONE
+TZID:Customized Time Zone
+BEGIN:STANDARD
+DTSTART:16010101T030000
+TZOFFSETFROM:+0200
+TZOFFSETTO:+0100
+RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=10
+END:STANDARD
+BEGIN:DAYLIGHT
+DTSTART:16010101T020000
+TZOFFSETFROM:+0100
+TZOFFSETTO:+0200
+RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=3
+END:DAYLIGHT
+END:VTIMEZONE
+BEGIN:VEVENT
+DESCRIPTION;LANGUAGE=de-DE:\n
+UID:040000008200E00074C5B7101A82E00800000000617EC2A24F5ED901000000000000000
+ 0100000005F326A277A3E8A4D8E8CA31C1AF73F5F
+SUMMARY;LANGUAGE=de-DE:Test
+DTSTART;TZID=Customized Time Zone:20230328T140000
+DTEND;TZID=Customized Time Zone:20230328T163000
+PRIORITY:5
+DTSTAMP:20230327T074734Z
+TRANSP:OPAQUE
+STATUS:CONFIRMED
+SEQUENCE:1
+LOCATION:Test location
+LAST-MODIFIED:20230329T082329Z
+CLASS:PRIVATE
+BEGIN:VALARM
+DESCRIPTION:REMINDER
+TRIGGER;RELATED=START:P
+ACTION:DISPLAY
+END:VALARM
+END:VEVENT
+END:VCALENDAR';
+
+        $oVCal = Reader::read($data);
+        self::assertEquals(new \DateInterval('PT0S'), $oVCal->VEVENT->VALARM->TRIGGER->getDateInterval());
+    }
+}
diff --git a/tests/VObject/Issue64Test.php b/tests/VObject/Issue64Test.php
index 2e623baa8..110f91fa2 100644
--- a/tests/VObject/Issue64Test.php
+++ b/tests/VObject/Issue64Test.php
@@ -6,14 +6,14 @@
 
 class Issue64Test extends TestCase
 {
-    public function testRead()
+    public function testRead(): void
     {
         $vcard = Reader::read(file_get_contents(dirname(__FILE__).'/issue64.vcf'));
-        $vcard = $vcard->convert(\Sabre\VObject\Document::VCARD30);
+        $vcard = $vcard->convert(Document::VCARD30);
         $vcard = $vcard->serialize();
 
         $converted = Reader::read($vcard);
 
-        $this->assertInstanceOf(Component\VCard::class, $converted);
+        self::assertInstanceOf(Component\VCard::class, $converted);
     }
 }
diff --git a/tests/VObject/Issue96Test.php b/tests/VObject/Issue96Test.php
index 88803a3e0..137149e8f 100644
--- a/tests/VObject/Issue96Test.php
+++ b/tests/VObject/Issue96Test.php
@@ -6,7 +6,7 @@
 
 class Issue96Test extends TestCase
 {
-    public function testRead()
+    public function testRead(): void
     {
         $input = <<<VCF
 BEGIN:VCARD
@@ -18,7 +18,7 @@ public function testRead()
 VCF;
 
         $vcard = Reader::read($input, Reader::OPTION_FORGIVING);
-        $this->assertInstanceOf(Component\VCard::class, $vcard);
-        $this->assertEquals('http://www.example.org', $vcard->URL->getValue());
+        self::assertInstanceOf(Component\VCard::class, $vcard);
+        self::assertEquals('http://www.example.org', $vcard->URL->getValue());
     }
 }
diff --git a/tests/VObject/IssueUndefinedIndexTest.php b/tests/VObject/IssueUndefinedIndexTest.php
index 7ed214a19..5085fbd20 100644
--- a/tests/VObject/IssueUndefinedIndexTest.php
+++ b/tests/VObject/IssueUndefinedIndexTest.php
@@ -6,7 +6,7 @@
 
 class IssueUndefinedIndexTest extends TestCase
 {
-    public function testRead()
+    public function testRead(): void
     {
         $this->expectException(ParseException::class);
         $input = <<<VCF
@@ -22,6 +22,6 @@ public function testRead()
 END:VCARD
 VCF;
 
-        $vcard = Reader::read($input, Reader::OPTION_FORGIVING);
+        Reader::read($input, Reader::OPTION_FORGIVING);
     }
 }
diff --git a/tests/VObject/JCalTest.php b/tests/VObject/JCalTest.php
index 9332b6413..fa3479665 100644
--- a/tests/VObject/JCalTest.php
+++ b/tests/VObject/JCalTest.php
@@ -6,7 +6,7 @@
 
 class JCalTest extends TestCase
 {
-    public function testToJCal()
+    public function testToJCal(): void
     {
         $cal = new Component\VCalendar();
 
@@ -144,6 +144,6 @@ public function testToJCal()
             ],
         ];
 
-        $this->assertEquals($expected, $cal->jsonSerialize());
+        self::assertEquals($expected, $cal->jsonSerialize());
     }
 }
diff --git a/tests/VObject/JCardTest.php b/tests/VObject/JCardTest.php
index 1864f666d..cbd56ba97 100644
--- a/tests/VObject/JCardTest.php
+++ b/tests/VObject/JCardTest.php
@@ -6,7 +6,7 @@
 
 class JCardTest extends TestCase
 {
-    public function testToJCard()
+    public function testToJCard(): void
     {
         $card = new Component\VCard([
             'VERSION' => '4.0',
@@ -189,6 +189,6 @@ public function testToJCard()
             ],
         ];
 
-        $this->assertEquals($expected, $card->jsonSerialize());
+        self::assertEquals($expected, $card->jsonSerialize());
     }
 }
diff --git a/tests/VObject/LineFoldingIssueTest.php b/tests/VObject/LineFoldingIssueTest.php
index 3d4f26af5..5e636d36c 100644
--- a/tests/VObject/LineFoldingIssueTest.php
+++ b/tests/VObject/LineFoldingIssueTest.php
@@ -6,7 +6,7 @@
 
 class LineFoldingIssueTest extends TestCase
 {
-    public function testRead()
+    public function testRead(): void
     {
         $event = <<<ICS
 BEGIN:VCALENDAR\r
@@ -18,6 +18,6 @@ public function testRead()
 ICS;
 
         $obj = Reader::read($event);
-        $this->assertEquals($event, $obj->serialize());
+        self::assertEquals($event, $obj->serialize());
     }
 }
diff --git a/tests/VObject/ParameterTest.php b/tests/VObject/ParameterTest.php
index 0e23b0620..4c9f2c774 100644
--- a/tests/VObject/ParameterTest.php
+++ b/tests/VObject/ParameterTest.php
@@ -6,79 +6,79 @@
 
 class ParameterTest extends TestCase
 {
-    public function testSetup()
+    public function testSetup(): void
     {
         $cal = new Component\VCalendar();
 
         $param = new Parameter($cal, 'name', 'value');
-        $this->assertEquals('NAME', $param->name);
-        $this->assertEquals('value', $param->getValue());
+        self::assertEquals('NAME', $param->name);
+        self::assertEquals('value', $param->getValue());
     }
 
-    public function testSetupNameLess()
+    public function testSetupNameLess(): void
     {
         $card = new Component\VCard();
 
         $param = new Parameter($card, null, 'URL');
-        $this->assertEquals('VALUE', $param->name);
-        $this->assertEquals('URL', $param->getValue());
-        $this->assertTrue($param->noName);
+        self::assertEquals('VALUE', $param->name);
+        self::assertEquals('URL', $param->getValue());
+        self::assertTrue($param->noName);
     }
 
-    public function testModify()
+    public function testModify(): void
     {
         $cal = new Component\VCalendar();
 
         $param = new Parameter($cal, 'name', null);
         $param->addValue(1);
-        $this->assertEquals([1], $param->getParts());
+        self::assertEquals([1], $param->getParts());
 
         $param->setParts([1, 2]);
-        $this->assertEquals([1, 2], $param->getParts());
+        self::assertEquals([1, 2], $param->getParts());
 
         $param->addValue(3);
-        $this->assertEquals([1, 2, 3], $param->getParts());
+        self::assertEquals([1, 2, 3], $param->getParts());
 
         $param->setValue(4);
         $param->addValue(5);
-        $this->assertEquals([4, 5], $param->getParts());
+        self::assertEquals([4, 5], $param->getParts());
     }
 
-    public function testCastToString()
+    public function testCastToString(): void
     {
         $cal = new Component\VCalendar();
         $param = new Parameter($cal, 'name', 'value');
-        $this->assertEquals('value', $param->__toString());
-        $this->assertEquals('value', (string) $param);
+        self::assertEquals('value', $param->__toString());
+        self::assertEquals('value', (string) $param);
     }
 
-    public function testCastNullToString()
+    public function testCastNullToString(): void
     {
         $cal = new Component\VCalendar();
         $param = new Parameter($cal, 'name', null);
-        $this->assertEquals('', $param->__toString());
-        $this->assertEquals('', (string) $param);
+        self::assertEquals('', $param->__toString());
+        self::assertEquals('', (string) $param);
     }
 
-    public function testSerialize()
+    public function testSerialize(): void
     {
         $cal = new Component\VCalendar();
         $param = new Parameter($cal, 'name', 'value');
-        $this->assertEquals('NAME=value', $param->serialize());
+        self::assertEquals('NAME=value', $param->serialize());
     }
 
-    public function testSerializeEmpty()
+    public function testSerializeEmpty(): void
     {
         $cal = new Component\VCalendar();
         $param = new Parameter($cal, 'name', null);
-        $this->assertEquals('NAME=', $param->serialize());
+        self::assertEquals('NAME=', $param->serialize());
     }
 
-    public function testSerializeComplex()
+    public function testSerializeComplex(): void
     {
         $cal = new Component\VCalendar();
         $param = new Parameter($cal, 'name', ['val1', 'val2;', 'val3^', "val4\n", 'val5"']);
-        $this->assertEquals('NAME=val1,"val2;","val3^^","val4^n","val5^\'"', $param->serialize());
+        self::assertEquals('NAME=val1,"val2;","val3^^","val4^n","val5^\'"', $param->serialize());
     }
 
     /**
@@ -87,14 +87,14 @@ public function testSerializeComplex()
      *
      * So we specifically added support for that.
      */
-    public function testSerializePlusSign()
+    public function testSerializePlusSign(): void
     {
         $cal = new Component\VCalendar();
         $param = new Parameter($cal, 'EMAIL', 'user+something@example.org');
-        $this->assertEquals('EMAIL="user+something@example.org"', $param->serialize());
+        self::assertEquals('EMAIL="user+something@example.org"', $param->serialize());
     }
 
-    public function testIterate()
+    public function testIterate(): void
     {
         $cal = new Component\VCalendar();
 
@@ -105,20 +105,20 @@ public function testIterate()
             $result[] = $value;
         }
 
-        $this->assertEquals([1, 2, 3, 4], $result);
+        self::assertEquals([1, 2, 3, 4], $result);
     }
 
-    public function testSerializeColon()
+    public function testSerializeColon(): void
     {
         $cal = new Component\VCalendar();
         $param = new Parameter($cal, 'name', 'va:lue');
-        $this->assertEquals('NAME="va:lue"', $param->serialize());
+        self::assertEquals('NAME="va:lue"', $param->serialize());
     }
 
-    public function testSerializeSemiColon()
+    public function testSerializeSemiColon(): void
     {
         $cal = new Component\VCalendar();
         $param = new Parameter($cal, 'name', 'va;lue');
-        $this->assertEquals('NAME="va;lue"', $param->serialize());
+        self::assertEquals('NAME="va;lue"', $param->serialize());
     }
 }
diff --git a/tests/VObject/Parser/JsonTest.php b/tests/VObject/Parser/JsonTest.php
index e1c701489..996e834e6 100644
--- a/tests/VObject/Parser/JsonTest.php
+++ b/tests/VObject/Parser/JsonTest.php
@@ -8,7 +8,7 @@
 
 class JsonTest extends TestCase
 {
-    public function testRoundTripJCard()
+    public function testRoundTripJCard(): void
     {
         $input = [
             'vcard',
@@ -189,15 +189,15 @@ public function testRoundTripJCard()
 END:VCARD
 
 VCF;
-        $this->assertEquals($expected, str_replace("\r", '', $result));
+        self::assertEquals($expected, str_replace("\r", '', $result));
 
-        $this->assertEquals(
+        self::assertEquals(
             $input,
             $vobj->jsonSerialize()
         );
     }
 
-    public function testRoundTripJCal()
+    public function testRoundTripJCal(): void
     {
         $input = [
             'vcalendar',
@@ -345,15 +345,15 @@ public function testRoundTripJCal()
 END:VCALENDAR
 
 VCF;
-        $this->assertEquals($expected, str_replace("\r", '', $result));
+        self::assertEquals($expected, str_replace("\r", '', $result));
 
-        $this->assertEquals(
+        self::assertEquals(
             $input,
             $vobj->jsonSerialize()
         );
     }
 
-    public function testParseStreamArg()
+    public function testParseStreamArg(): void
     {
         $input = [
             'vcard',
@@ -369,10 +369,10 @@ public function testParseStreamArg()
         rewind($stream);
 
         $result = VObject\Reader::readJson($stream, 0);
-        $this->assertEquals('foo', $result->FN->getValue());
+        self::assertEquals('foo', $result->FN->getValue());
     }
 
-    public function testParseInvalidData()
+    public function testParseInvalidData(): void
     {
         $this->expectException(ParseException::class);
         $json = new Json();
diff --git a/tests/VObject/Parser/MimeDirTest.php b/tests/VObject/Parser/MimeDirTest.php
index 183c9ce4c..24656f886 100644
--- a/tests/VObject/Parser/MimeDirTest.php
+++ b/tests/VObject/Parser/MimeDirTest.php
@@ -3,6 +3,7 @@
 namespace Sabre\VObject\Parser;
 
 use PHPUnit\Framework\TestCase;
+use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\ParseException;
 
 /**
@@ -11,14 +12,14 @@
  */
 class MimeDirTest extends TestCase
 {
-    public function testParseError()
+    public function testParseError(): void
     {
         $this->expectException(ParseException::class);
         $mimeDir = new MimeDir();
         $mimeDir->parse(fopen(__FILE__, 'a+'));
     }
 
-    public function testDecodeLatin1()
+    public function testDecodeLatin1(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -30,10 +31,10 @@ public function testDecodeLatin1()
         $mimeDir = new MimeDir();
         $mimeDir->setCharset('ISO-8859-1');
         $vcard = $mimeDir->parse($vcard);
-        $this->assertEquals("umlaut u - \xC3\xBC", $vcard->FN->getValue());
+        self::assertEquals("umlaut u - \xC3\xBC", $vcard->FN->getValue());
     }
 
-    public function testDecodeInlineLatin1()
+    public function testDecodeInlineLatin1(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -44,10 +45,10 @@ public function testDecodeInlineLatin1()
 
         $mimeDir = new MimeDir();
         $vcard = $mimeDir->parse($vcard);
-        $this->assertEquals("umlaut u - \xC3\xBC", $vcard->FN->getValue());
+        self::assertEquals("umlaut u - \xC3\xBC", $vcard->FN->getValue());
     }
 
-    public function testIgnoreCharsetVCard30()
+    public function testIgnoreCharsetVCard30(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -58,10 +59,10 @@ public function testIgnoreCharsetVCard30()
 
         $mimeDir = new MimeDir();
         $vcard = $mimeDir->parse($vcard);
-        $this->assertEquals("foo-bar - \xFC", $vcard->FN->getValue());
+        self::assertEquals("foo-bar - \xFC", $vcard->FN->getValue());
     }
 
-    public function testDontDecodeLatin1()
+    public function testDontDecodeLatin1(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -76,17 +77,17 @@ public function testDontDecodeLatin1()
         // the encoding was set to UTF-8. The result is actually invalid
         // and the validator should report this, but it tests effectively
         // that we pass through the string byte-by-byte.
-        $this->assertEquals("umlaut u - \xFC", $vcard->FN->getValue());
+        self::assertEquals("umlaut u - \xFC", $vcard->FN->getValue());
     }
 
-    public function testDecodeUnsupportedCharset()
+    public function testDecodeUnsupportedCharset(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $mimeDir = new MimeDir();
         $mimeDir->setCharset('foobar');
     }
 
-    public function testDecodeUnsupportedInlineCharset()
+    public function testDecodeUnsupportedInlineCharset(): void
     {
         $this->expectException(ParseException::class);
         $vcard = <<<VCF
@@ -100,7 +101,7 @@ public function testDecodeUnsupportedInlineCharset()
         $mimeDir->parse($vcard);
     }
 
-    public function testDecodeWindows1252()
+    public function testDecodeWindows1252(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -112,10 +113,10 @@ public function testDecodeWindows1252()
         $mimeDir = new MimeDir();
         $mimeDir->setCharset('Windows-1252');
         $vcard = $mimeDir->parse($vcard);
-        $this->assertEquals("Euro \xE2\x82\xAC", $vcard->FN->getValue());
+        self::assertEquals("Euro \xE2\x82\xAC", $vcard->FN->getValue());
     }
 
-    public function testDecodeWindows1252Inline()
+    public function testDecodeWindows1252Inline(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -126,10 +127,10 @@ public function testDecodeWindows1252Inline()
 
         $mimeDir = new MimeDir();
         $vcard = $mimeDir->parse($vcard);
-        $this->assertEquals("Euro \xE2\x82\xAC", $vcard->FN->getValue());
+        self::assertEquals("Euro \xE2\x82\xAC", $vcard->FN->getValue());
     }
 
-    public function testCaseInsensitiveInlineCharset()
+    public function testCaseInsensitiveInlineCharset(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -142,7 +143,101 @@ public function testCaseInsensitiveInlineCharset()
         $mimeDir = new MimeDir();
         $vcard = $mimeDir->parse($vcard);
         // we can do a simple assertion here. As long as we don't get an exception, everything is thing
-        $this->assertEquals('Euro', $vcard->FN->getValue());
-        $this->assertEquals('Test2', $vcard->N->getValue());
+        self::assertEquals('Euro', $vcard->FN->getValue());
+        self::assertEquals('Test2', $vcard->N->getValue());
+    }
+
+    public function testParsingTwiceSameContent(): void
+    {
+        $card = <<<EOF
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:PRODID
+BEGIN:VEVENT
+DTSTAMP;TZID=Europe/Busingen:20220712T172312
+UID:UID
+DTSTART;VALUE=DATE;VALUE=DATE;VALUE=DATE:20220612
+END:VEVENT
+END:VCALENDAR
+EOF;
+
+        $mimeDir = new MimeDir();
+        $vcard = $mimeDir->parse($card);
+        // we can do a simple assertion here. As long as we don't get an exception, everything is fine
+        self::assertEquals('20220612', $vcard->VEVENT->DTSTART->getValue());
+    }
+
+    /**
+     * @covers \Sabre\VObject\Parser\MimeDir::readProperty
+     *
+     * @dataProvider provideBrokenVCalendar
+     */
+    public function testBrokenMultilineContentDoesNotBreakImportWhenSetToIgnoreBrokenLines(string $vcalendar): void
+    {
+        $mimeDir = new MimeDir(null, MimeDir::OPTION_IGNORE_INVALID_LINES);
+        $vcalendar = $mimeDir->parse($vcalendar);
+        self::assertInstanceOf(VCalendar::class, $vcalendar);
+    }
+
+    /**
+     * @covers \Sabre\VObject\Parser\MimeDir::readProperty
+     *
+     * @dataProvider provideBrokenVCalendar
+     *
+     * @param string $vcalendar
+     */
+    public function testBrokenMultilineContentDoesBreakImport($vcalendar): void
+    {
+        $mimeDir = new MimeDir();
+        $this->expectException(ParseException::class);
+        $mimeDir->parse($vcalendar);
+    }
+
+    public function provideBrokenVCalendar(): array
+    {
+        return [[<<<EOF
+BEGIN:VCALENDAR
+BEGIN:VEVENT
+CREATED:20160501T180854Z
+UID:15C11082-9FC5-4159-A888-4A4B92D0DB71
+DTEND;TZID=America/Los_Angeles:20160504T133000
+SUMMARY:Interment
+DTSTART;TZID=America/Los_Angeles:20160504T123000
+DTSTAMP:20160501T180924Z
+X-APPLE-STRUCTURED-LOCATION;VALUE=URI;X-APPLE-MAPKIT-HANDLE=CAES8gEaEglZw
+ 0Xu6epCQBFdwwyNJ49ewCKOAQoNVW5pdGVkIFN0YXRlcxICVVMaCkNhbGlmb3JuaWEiAkNBK
+ gdBbGFtZWRhMgdPYWtsYW5kOgU5NDYxMVIMUGllZG1vbnQgQXZlWgQ1MDAwYhE1MDAwIFBpZ
+ WRtb250IEF2ZWoENDIyMHIWTW91bnRhaW4gVmlldyBDZW1ldGVyeaIBCjk0NjExLTQyMjAqE
+ TUwMDAgUGllZG1vbnQgQXZlMhE1MDAwIFBpZWRtb250IEF2ZTIST2FrbGFuZCwgQ0EgIDk0N
+ jExMg1Vbml0ZWQgU3RhdGVzODlAAA==;X-APPLE-RADIUS=1001.127625592278;X-TITLE
+ =Mountain View Cemetery:5000 Piedmont Avenue
+OAKLAND, CA 94611
+SEQUENCE:0
+END:VEVENT
+END:VCALENDAR
+EOF
+        ], [
+            <<<EOF
+BEGIN:VCALENDAR
+BEGIN:VEVENT
+CREATED:20160501T180854Z
+UID:15C11082-9FC5-4159-A888-4A4B92D0DB71
+DTEND;TZID=America/Los_Angeles:20160504T133000
+SUMMARY:Interment
+DTSTART;TZID=America/Los_Angeles:20160504T123000
+DTSTAMP:20160501T180924Z
+X-APPLE-STRUCTURED-LOCATION;VALUE=URI;X-APPLE-MAPKIT-HANDLE=CAES8gEaEglZw
+ 0Xu6epCQBFdwwyNJ49ewCKOAQoNVW5pdGVkIFN0YXRlcxICVVMaCkNhbGlmb3JuaWEiAkNBK
+ gdBbGFtZWRhMgdPYWtsYW5kOgU5NDYxMVIMUGllZG1vbnQgQXZlWgQ1MDAwYhE1MDAwIFBpZ
+ WRtb250IEF2ZWoENDIyMHIWTW91bnRhaW4gVmlldyBDZW1ldGVyeaIBCjk0NjExLTQyMjAqE
+ TUwMDAgUGllZG1vbnQgQXZlMhE1MDAwIFBpZWRtb250IEF2ZTIST2FrbGFuZCwgQ0EgIDk0N
+ jExMg1Vbml0ZWQgU3RhdGVzODlAAA==;X-APPLE-RADIUS=1001.127625592278;X-TITLE
+ =Mountain View Cemetery:5000 Piedmont Avenue
+OAKLAND, CA 94611:
+SEQUENCE:0
+END:VEVENT
+END:VCALENDAR
+EOF
+        ]];
     }
 }
diff --git a/tests/VObject/Parser/QuotedPrintableTest.php b/tests/VObject/Parser/QuotedPrintableTest.php
index 7cadb46eb..e8153604d 100644
--- a/tests/VObject/Parser/QuotedPrintableTest.php
+++ b/tests/VObject/Parser/QuotedPrintableTest.php
@@ -4,56 +4,57 @@
 
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component;
+use Sabre\VObject\Property;
 use Sabre\VObject\Reader;
 
 class QuotedPrintableTest extends TestCase
 {
-    public function testReadQuotedPrintableSimple()
+    public function testReadQuotedPrintableSimple(): void
     {
         $data = "BEGIN:VCARD\r\nLABEL;ENCODING=QUOTED-PRINTABLE:Aach=65n\r\nEND:VCARD";
 
         $result = Reader::read($data);
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCARD', $result->name);
-        $this->assertEquals(1, count($result->children()));
-        $this->assertEquals('Aachen', $this->getPropertyValue($result->LABEL));
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCARD', $result->name);
+        self::assertCount(1, $result->children());
+        self::assertEquals('Aachen', $this->getPropertyValue($result->LABEL));
     }
 
-    public function testReadQuotedPrintableNewlineSoft()
+    public function testReadQuotedPrintableNewlineSoft(): void
     {
         $data = "BEGIN:VCARD\r\nLABEL;ENCODING=QUOTED-PRINTABLE:Aa=\r\n ch=\r\n en\r\nEND:VCARD";
         $result = Reader::read($data);
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCARD', $result->name);
-        $this->assertEquals(1, count($result->children()));
-        $this->assertEquals('Aachen', $this->getPropertyValue($result->LABEL));
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCARD', $result->name);
+        self::assertCount(1, $result->children());
+        self::assertEquals('Aachen', $this->getPropertyValue($result->LABEL));
     }
 
-    public function testReadQuotedPrintableNewlineHard()
+    public function testReadQuotedPrintableNewlineHard(): void
     {
         $data = "BEGIN:VCARD\r\nLABEL;ENCODING=QUOTED-PRINTABLE:Aachen=0D=0A=\r\n Germany\r\nEND:VCARD";
         $result = Reader::read($data);
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCARD', $result->name);
-        $this->assertEquals(1, count($result->children()));
-        $this->assertEquals("Aachen\r\nGermany", $this->getPropertyValue($result->LABEL));
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCARD', $result->name);
+        self::assertCount(1, $result->children());
+        self::assertEquals("Aachen\r\nGermany", $this->getPropertyValue($result->LABEL));
     }
 
-    public function testReadQuotedPrintableCompatibilityMS()
+    public function testReadQuotedPrintableCompatibilityMS(): void
     {
         $data = "BEGIN:VCARD\r\nLABEL;ENCODING=QUOTED-PRINTABLE:Aachen=0D=0A=\r\nDeutschland:okay\r\nEND:VCARD";
         $result = Reader::read($data, Reader::OPTION_FORGIVING);
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCARD', $result->name);
-        $this->assertEquals(1, count($result->children()));
-        $this->assertEquals("Aachen\r\nDeutschland:okay", $this->getPropertyValue($result->LABEL));
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCARD', $result->name);
+        self::assertCount(1, $result->children());
+        self::assertEquals("Aachen\r\nDeutschland:okay", $this->getPropertyValue($result->LABEL));
     }
 
-    public function testReadQuotesPrintableCompoundValues()
+    public function testReadQuotesPrintableCompoundValues(): void
     {
         $data = <<<VCF
 BEGIN:VCARD
@@ -66,12 +67,12 @@ public function testReadQuotesPrintableCompoundValues()
 VCF;
 
         $result = Reader::read($data, Reader::OPTION_FORGIVING);
-        $this->assertEquals([
+        self::assertEquals([
             '', '', 'Münster Str. 1', 'Münster', '', '48143', 'Deutschland',
         ], $result->ADR->getParts());
     }
 
-    private function getPropertyValue(\Sabre\VObject\Property $property)
+    private function getPropertyValue(Property $property): string
     {
         return (string) $property;
 
diff --git a/tests/VObject/Parser/XmlTest.php b/tests/VObject/Parser/XmlTest.php
index 46ee30ce2..2276f7fdf 100644
--- a/tests/VObject/Parser/XmlTest.php
+++ b/tests/VObject/Parser/XmlTest.php
@@ -9,10 +9,10 @@ class XmlTest extends TestCase
 {
     use VObject\PHPUnitAssertions;
 
-    public function testRFC6321Example1()
+    public function testRFC6321Example1(): void
     {
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -48,7 +48,7 @@ public function testRFC6321Example1()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             // VERSION comes first because this is required by vCard 4.0.
             'VERSION:2.0'."\n".
@@ -64,7 +64,7 @@ public function testRFC6321Example1()
         );
     }
 
-    public function testRFC6321Example2()
+    public function testRFC6321Example2(): void
     {
         $xml = <<<XML
 <?xml version="1.0" encoding="UTF-8" ?>
@@ -212,7 +212,7 @@ public function testRFC6321Example2()
 XML;
 
         $component = VObject\Reader::readXML($xml);
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             'BEGIN:VCALENDAR'."\n".
             'VERSION:2.0'."\n".
             'PRODID:-//Example Inc.//Example Client//EN'."\n".
@@ -262,16 +262,16 @@ public function testRFC6321Example2()
     /**
      * iCalendar Stream.
      */
-    public function testRFC6321Section3Part2()
+    public function testRFC6321Section3Part2(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar/>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'END:VCALENDAR'."\n"
         );
@@ -280,10 +280,10 @@ public function testRFC6321Section3Part2()
     /**
      * All components exist.
      */
-    public function testRFC6321Section3Part3()
+    public function testRFC6321Section3Part3(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -300,7 +300,7 @@ public function testRFC6321Section3Part3()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'BEGIN:VTIMEZONE'."\n".
             'END:VTIMEZONE'."\n".
@@ -325,10 +325,10 @@ public function testRFC6321Section3Part3()
     /**
      * Properties, Special Cases, GEO.
      */
-    public function testRFC6321Section3Part4Part1Part2()
+    public function testRFC6321Section3Part4Part1Part2(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -341,7 +341,7 @@ public function testRFC6321Section3Part4Part1Part2()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'GEO:37.386013;-122.082932'."\n".
             'END:VCALENDAR'."\n"
@@ -351,11 +351,11 @@ public function testRFC6321Section3Part4Part1Part2()
     /**
      * Properties, Special Cases, REQUEST-STATUS.
      */
-    public function testRFC6321Section3Part4Part1Part3()
+    public function testRFC6321Section3Part4Part1Part3(): void
     {
         // Example 1 of RFC5545, Section 3.8.8.3.
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -368,15 +368,15 @@ public function testRFC6321Section3Part4Part1Part3()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'REQUEST-STATUS:2.0;Success'."\n".
             'END:VCALENDAR'."\n"
         );
 
         // Example 2 of RFC5545, Section 3.8.8.3.
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -390,15 +390,15 @@ public function testRFC6321Section3Part4Part1Part3()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'REQUEST-STATUS:3.1;Invalid property value;DTSTART:96-Apr-01'."\n".
             'END:VCALENDAR'."\n"
         );
 
         // Example 3 of RFC5545, Section 3.8.8.3.
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -412,7 +412,7 @@ public function testRFC6321Section3Part4Part1Part3()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'REQUEST-STATUS:2.8;Success\, repeating event ignored. Scheduled as a single'."\n".
             '  event.;RRULE:FREQ=WEEKLY\;INTERVAL=2'."\n".
@@ -420,8 +420,8 @@ public function testRFC6321Section3Part4Part1Part3()
         );
 
         // Example 4 of RFC5545, Section 3.8.8.3.
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -434,15 +434,15 @@ public function testRFC6321Section3Part4Part1Part3()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'REQUEST-STATUS:4.1;Event conflict.  Date-time is busy.'."\n".
             'END:VCALENDAR'."\n"
         );
 
         // Example 5 of RFC5545, Section 3.8.8.3.
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -456,7 +456,7 @@ public function testRFC6321Section3Part4Part1Part3()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'REQUEST-STATUS:3.7;Invalid calendar user;ATTENDEE:mailto:jsmith@example.com'."\n".
             'END:VCALENDAR'."\n"
@@ -466,10 +466,10 @@ public function testRFC6321Section3Part4Part1Part3()
     /**
      * Values, Binary.
      */
-    public function testRFC6321Section3Part6Part1()
+    public function testRFC6321Section3Part6Part1(): void
     {
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -481,15 +481,15 @@ public function testRFC6321Section3Part6Part1()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'ATTACH:SGVsbG8gV29ybGQh'."\n".
             'END:VCALENDAR'."\n"
         );
 
         // In vCard 4, BINARY no longer exists and is replaced by URI.
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -501,7 +501,7 @@ public function testRFC6321Section3Part6Part1()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'ATTACH:SGVsbG8gV29ybGQh'."\n".
             'END:VCALENDAR'."\n"
@@ -511,10 +511,10 @@ public function testRFC6321Section3Part6Part1()
     /**
      * Values, Boolean.
      */
-    public function testRFC6321Section3Part6Part2()
+    public function testRFC6321Section3Part6Part2(): void
     {
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -529,7 +529,7 @@ public function testRFC6321Section3Part6Part2()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'ATTENDEE;RSVP=true:mailto:cyrus@example.com'."\n".
             'END:VCALENDAR'."\n"
@@ -539,10 +539,10 @@ public function testRFC6321Section3Part6Part2()
     /**
      * Values, Calendar User Address.
      */
-    public function testRFC6321Section3Part6Part3()
+    public function testRFC6321Section3Part6Part3(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -554,7 +554,7 @@ public function testRFC6321Section3Part6Part3()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'ATTENDEE:mailto:cyrus@example.com'."\n".
             'END:VCALENDAR'."\n"
@@ -564,10 +564,10 @@ public function testRFC6321Section3Part6Part3()
     /**
      * Values, Date.
      */
-    public function testRFC6321Section3Part6Part4()
+    public function testRFC6321Section3Part6Part4(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -579,7 +579,7 @@ public function testRFC6321Section3Part6Part4()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'DTSTART;VALUE=DATE:20110517'."\n".
             'END:VCALENDAR'."\n"
@@ -589,10 +589,10 @@ public function testRFC6321Section3Part6Part4()
     /**
      * Values, Date-Time.
      */
-    public function testRFC6321Section3Part6Part5()
+    public function testRFC6321Section3Part6Part5(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -604,7 +604,7 @@ public function testRFC6321Section3Part6Part5()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'DTSTART:20110517T120000'."\n".
             'END:VCALENDAR'."\n"
@@ -614,10 +614,10 @@ public function testRFC6321Section3Part6Part5()
     /**
      * Values, Duration.
      */
-    public function testRFC6321Section3Part6Part6()
+    public function testRFC6321Section3Part6Part6(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -629,7 +629,7 @@ public function testRFC6321Section3Part6Part6()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'DURATION:P1D'."\n".
             'END:VCALENDAR'."\n"
@@ -639,7 +639,7 @@ public function testRFC6321Section3Part6Part6()
     /**
      * Values, Float.
      */
-    public function testRFC6321Section3Part6Part7()
+    public function testRFC6321Section3Part6Part7(): void
     {
         // GEO uses <float /> with a positive and a non-negative numbers.
         $this->testRFC6321Section3Part4Part1Part2();
@@ -648,10 +648,10 @@ public function testRFC6321Section3Part6Part7()
     /**
      * Values, Integer.
      */
-    public function testRFC6321Section3Part6Part8()
+    public function testRFC6321Section3Part6Part8(): void
     {
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -663,14 +663,14 @@ public function testRFC6321Section3Part6Part8()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'FOO:42'."\n".
             'END:VCALENDAR'."\n"
         );
 
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -682,7 +682,7 @@ public function testRFC6321Section3Part6Part8()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'FOO:-42'."\n".
             'END:VCALENDAR'."\n"
@@ -692,10 +692,10 @@ public function testRFC6321Section3Part6Part8()
     /**
      * Values, Period of Time.
      */
-    public function testRFC6321Section3Part6Part9()
+    public function testRFC6321Section3Part6Part9(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -710,14 +710,14 @@ public function testRFC6321Section3Part6Part9()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'FREEBUSY:20110517T120000/P1H'."\n".
             'END:VCALENDAR'."\n"
         );
 
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -732,7 +732,7 @@ public function testRFC6321Section3Part6Part9()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'FREEBUSY:20110517T120000/20120517T120000'."\n".
             'END:VCALENDAR'."\n"
@@ -742,10 +742,10 @@ public function testRFC6321Section3Part6Part9()
     /**
      * Values, Recurrence Rule.
      */
-    public function testRFC6321Section3Part6Part10()
+    public function testRFC6321Section3Part6Part10(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -762,7 +762,7 @@ public function testRFC6321Section3Part6Part10()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'RRULE:FREQ=YEARLY;COUNT=5;BYDAY=-1SU;BYMONTH=10'."\n".
             'END:VCALENDAR'."\n"
@@ -772,10 +772,10 @@ public function testRFC6321Section3Part6Part10()
     /**
      * Values, Text.
      */
-    public function testRFC6321Section3Part6Part11()
+    public function testRFC6321Section3Part6Part11(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -787,7 +787,7 @@ public function testRFC6321Section3Part6Part11()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'CALSCALE:GREGORIAN'."\n".
             'END:VCALENDAR'."\n"
@@ -797,10 +797,10 @@ public function testRFC6321Section3Part6Part11()
     /**
      * Values, Time.
      */
-    public function testRFC6321Section3Part6Part12()
+    public function testRFC6321Section3Part6Part12(): void
     {
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -812,7 +812,7 @@ public function testRFC6321Section3Part6Part12()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'FOO:120000'."\n".
             'END:VCALENDAR'."\n"
@@ -822,10 +822,10 @@ public function testRFC6321Section3Part6Part12()
     /**
      * Values, URI.
      */
-    public function testRFC6321Section3Part6Part13()
+    public function testRFC6321Section3Part6Part13(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -837,7 +837,7 @@ public function testRFC6321Section3Part6Part13()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'ATTACH:http://calendar.example.com'."\n".
             'END:VCALENDAR'."\n"
@@ -847,11 +847,11 @@ public function testRFC6321Section3Part6Part13()
     /**
      * Values, UTC Offset.
      */
-    public function testRFC6321Section3Part6Part14()
+    public function testRFC6321Section3Part6Part14(): void
     {
         // Example 1 of RFC5545, Section 3.3.14.
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -863,15 +863,15 @@ public function testRFC6321Section3Part6Part14()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'TZOFFSETFROM:-0500'."\n".
             'END:VCALENDAR'."\n"
         );
 
         // Example 2 of RFC5545, Section 3.3.14.
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -883,7 +883,7 @@ public function testRFC6321Section3Part6Part14()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'TZOFFSETFROM:+0100'."\n".
             'END:VCALENDAR'."\n"
@@ -893,10 +893,10 @@ public function testRFC6321Section3Part6Part14()
     /**
      * Handling Unrecognized Properties or Parameters.
      */
-    public function testRFC6321Section5()
+    public function testRFC6321Section5(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -908,14 +908,14 @@ public function testRFC6321Section5()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'X-PROPERTY:20110512T120000Z'."\n".
             'END:VCALENDAR'."\n"
         );
 
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -932,17 +932,17 @@ public function testRFC6321Section5()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'DTSTART;X-PARAM=PT30M:20110512T130000Z'."\n".
             'END:VCALENDAR'."\n"
         );
     }
 
-    public function testRDateWithDateTime()
+    public function testRDateWithDateTime(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -954,14 +954,14 @@ public function testRDateWithDateTime()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'RDATE:20080205T191224Z'."\n".
             'END:VCALENDAR'."\n"
         );
 
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -974,17 +974,17 @@ public function testRDateWithDateTime()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'RDATE:20080205T191224Z,20090205T191224Z'."\n".
             'END:VCALENDAR'."\n"
         );
     }
 
-    public function testRDateWithDate()
+    public function testRDateWithDate(): void
     {
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -996,14 +996,14 @@ public function testRDateWithDate()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'RDATE:20081006'."\n".
             'END:VCALENDAR'."\n"
         );
 
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -1017,17 +1017,17 @@ public function testRDateWithDate()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'RDATE:20081006,20091006,20101006'."\n".
             'END:VCALENDAR'."\n"
         );
     }
 
-    public function testRDateWithPeriod()
+    public function testRDateWithPeriod(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -1047,14 +1047,14 @@ public function testRDateWithPeriod()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'RDATE;TZID=US/Eastern;VALUE=PERIOD:20060102T150000/PT2H'."\n".
             'END:VCALENDAR'."\n"
         );
 
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
  <vcalendar>
@@ -1078,7 +1078,7 @@ public function testRDateWithPeriod()
  </vcalendar>
 </icalendar>
 XML
-,
+            ,
             'BEGIN:VCALENDAR'."\n".
             'RDATE;TZID=US/Eastern;VALUE=PERIOD:20060102T150000/PT2H,20080102T150000/PT1'."\n".
             ' H'."\n".
@@ -1089,10 +1089,10 @@ public function testRDateWithPeriod()
     /**
      * Basic example.
      */
-    public function testRFC6351Basic()
+    public function testRFC6351Basic(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1109,7 +1109,7 @@ public function testRFC6351Basic()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'FN:J. Doe'."\n".
@@ -1121,10 +1121,10 @@ public function testRFC6351Basic()
     /**
      * Example 1.
      */
-    public function testRFC6351Example1()
+    public function testRFC6351Example1(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1150,7 +1150,7 @@ public function testRFC6351Example1()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'FN:J. Doe'."\n".
@@ -1165,10 +1165,10 @@ public function testRFC6351Example1()
     /**
      * Design Considerations.
      */
-    public function testRFC6351Section5()
+    public function testRFC6351Section5(): void
     {
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1184,15 +1184,15 @@ public function testRFC6351Section5()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'TEL;TYPE="voice,video":tel:+1-555-555-555'."\n".
             'END:VCARD'."\n"
         );
 
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1208,7 +1208,7 @@ public function testRFC6351Section5()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'TEL;TYPE="voice,video":tel:+1-555-555-555'."\n".
@@ -1219,10 +1219,10 @@ public function testRFC6351Section5()
     /**
      * Design Considerations.
      */
-    public function testRFC6351Section5Group()
+    public function testRFC6351Section5Group(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1245,7 +1245,7 @@ public function testRFC6351Section5Group()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'TEL:tel:+1-555-555-556'."\n".
@@ -1259,10 +1259,10 @@ public function testRFC6351Section5Group()
     /**
      * Extensibility.
      */
-    public function testRFC6351Section5Part1NoNamespace()
+    public function testRFC6351Section5Part1NoNamespace(): void
     {
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1277,7 +1277,7 @@ public function testRFC6351Section5Part1NoNamespace()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'X-MY-PROP;PREF=1:value goes here'."\n".
@@ -1288,10 +1288,10 @@ public function testRFC6351Section5Part1NoNamespace()
     /**
      * Section 4.3.1 of Relax NG Schema: value-date.
      */
-    public function testRFC6351ValueDateWithYearMonthDay()
+    public function testRFC6351ValueDateWithYearMonthDay(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1301,7 +1301,7 @@ public function testRFC6351ValueDateWithYearMonthDay()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:20150128'."\n".
@@ -1312,10 +1312,10 @@ public function testRFC6351ValueDateWithYearMonthDay()
     /**
      * Section 4.3.1 of Relax NG Schema: value-date.
      */
-    public function testRFC6351ValueDateWithYearMonth()
+    public function testRFC6351ValueDateWithYearMonth(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1325,7 +1325,7 @@ public function testRFC6351ValueDateWithYearMonth()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:2015-01'."\n".
@@ -1336,10 +1336,10 @@ public function testRFC6351ValueDateWithYearMonth()
     /**
      * Section 4.3.1 of Relax NG Schema: value-date.
      */
-    public function testRFC6351ValueDateWithMonth()
+    public function testRFC6351ValueDateWithMonth(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1349,7 +1349,7 @@ public function testRFC6351ValueDateWithMonth()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:--01'."\n".
@@ -1360,10 +1360,10 @@ public function testRFC6351ValueDateWithMonth()
     /**
      * Section 4.3.1 of Relax NG Schema: value-date.
      */
-    public function testRFC6351ValueDateWithMonthDay()
+    public function testRFC6351ValueDateWithMonthDay(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1373,7 +1373,7 @@ public function testRFC6351ValueDateWithMonthDay()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:--0128'."\n".
@@ -1384,10 +1384,10 @@ public function testRFC6351ValueDateWithMonthDay()
     /**
      * Section 4.3.1 of Relax NG Schema: value-date.
      */
-    public function testRFC6351ValueDateWithDay()
+    public function testRFC6351ValueDateWithDay(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1397,7 +1397,7 @@ public function testRFC6351ValueDateWithDay()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:---28'."\n".
@@ -1408,10 +1408,10 @@ public function testRFC6351ValueDateWithDay()
     /**
      * Section 4.3.2 of Relax NG Schema: value-time.
      */
-    public function testRFC6351ValueTimeWithHour()
+    public function testRFC6351ValueTimeWithHour(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1421,7 +1421,7 @@ public function testRFC6351ValueTimeWithHour()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:13'."\n".
@@ -1432,10 +1432,10 @@ public function testRFC6351ValueTimeWithHour()
     /**
      * Section 4.3.2 of Relax NG Schema: value-time.
      */
-    public function testRFC6351ValueTimeWithHourMinute()
+    public function testRFC6351ValueTimeWithHourMinute(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1445,7 +1445,7 @@ public function testRFC6351ValueTimeWithHourMinute()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:1353'."\n".
@@ -1456,10 +1456,10 @@ public function testRFC6351ValueTimeWithHourMinute()
     /**
      * Section 4.3.2 of Relax NG Schema: value-time.
      */
-    public function testRFC6351ValueTimeWithHourMinuteSecond()
+    public function testRFC6351ValueTimeWithHourMinuteSecond(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1469,7 +1469,7 @@ public function testRFC6351ValueTimeWithHourMinuteSecond()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:135301'."\n".
@@ -1480,10 +1480,10 @@ public function testRFC6351ValueTimeWithHourMinuteSecond()
     /**
      * Section 4.3.2 of Relax NG Schema: value-time.
      */
-    public function testRFC6351ValueTimeWithMinute()
+    public function testRFC6351ValueTimeWithMinute(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1493,7 +1493,7 @@ public function testRFC6351ValueTimeWithMinute()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:-53'."\n".
@@ -1504,10 +1504,10 @@ public function testRFC6351ValueTimeWithMinute()
     /**
      * Section 4.3.2 of Relax NG Schema: value-time.
      */
-    public function testRFC6351ValueTimeWithMinuteSecond()
+    public function testRFC6351ValueTimeWithMinuteSecond(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1517,7 +1517,7 @@ public function testRFC6351ValueTimeWithMinuteSecond()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:-5301'."\n".
@@ -1528,9 +1528,9 @@ public function testRFC6351ValueTimeWithMinuteSecond()
     /**
      * Section 4.3.2 of Relax NG Schema: value-time.
      */
-    public function testRFC6351ValueTimeWithSecond()
+    public function testRFC6351ValueTimeWithSecond(): void
     {
-        $this->assertTrue(true);
+        self::assertTrue(true);
 
         /*
          * According to the Relax NG Schema, there is a conflict between
@@ -1538,7 +1538,7 @@ public function testRFC6351ValueTimeWithSecond()
          * value-date because of the higher priority set in
          * value-date-and-or-time. So we basically skip this test.
          *
-        $this->assertXMLReflexivelyEqualsToMimeDir(
+        self::assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
@@ -1561,10 +1561,10 @@ public function testRFC6351ValueTimeWithSecond()
     /**
      * Section 4.3.2 of Relax NG Schema: value-time.
      */
-    public function testRFC6351ValueTimeWithSecondZ()
+    public function testRFC6351ValueTimeWithSecondZ(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1574,7 +1574,7 @@ public function testRFC6351ValueTimeWithSecondZ()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:--01Z'."\n".
@@ -1585,10 +1585,10 @@ public function testRFC6351ValueTimeWithSecondZ()
     /**
      * Section 4.3.2 of Relax NG Schema: value-time.
      */
-    public function testRFC6351ValueTimeWithSecondTZ()
+    public function testRFC6351ValueTimeWithSecondTZ(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1598,7 +1598,7 @@ public function testRFC6351ValueTimeWithSecondTZ()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:--01+1234'."\n".
@@ -1609,10 +1609,10 @@ public function testRFC6351ValueTimeWithSecondTZ()
     /**
      * Section 4.3.3 of Relax NG Schema: value-date-time.
      */
-    public function testRFC6351ValueDateTimeWithYearMonthDayHour()
+    public function testRFC6351ValueDateTimeWithYearMonthDayHour(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1622,7 +1622,7 @@ public function testRFC6351ValueDateTimeWithYearMonthDayHour()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:20150128T13'."\n".
@@ -1633,10 +1633,10 @@ public function testRFC6351ValueDateTimeWithYearMonthDayHour()
     /**
      * Section 4.3.3 of Relax NG Schema: value-date-time.
      */
-    public function testRFC6351ValueDateTimeWithMonthDayHour()
+    public function testRFC6351ValueDateTimeWithMonthDayHour(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1646,7 +1646,7 @@ public function testRFC6351ValueDateTimeWithMonthDayHour()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:--0128T13'."\n".
@@ -1657,10 +1657,10 @@ public function testRFC6351ValueDateTimeWithMonthDayHour()
     /**
      * Section 4.3.3 of Relax NG Schema: value-date-time.
      */
-    public function testRFC6351ValueDateTimeWithDayHour()
+    public function testRFC6351ValueDateTimeWithDayHour(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1670,7 +1670,7 @@ public function testRFC6351ValueDateTimeWithDayHour()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:---28T13'."\n".
@@ -1681,10 +1681,10 @@ public function testRFC6351ValueDateTimeWithDayHour()
     /**
      * Section 4.3.3 of Relax NG Schema: value-date-time.
      */
-    public function testRFC6351ValueDateTimeWithDayHourMinute()
+    public function testRFC6351ValueDateTimeWithDayHourMinute(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1694,7 +1694,7 @@ public function testRFC6351ValueDateTimeWithDayHourMinute()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:---28T1353'."\n".
@@ -1705,10 +1705,10 @@ public function testRFC6351ValueDateTimeWithDayHourMinute()
     /**
      * Section 4.3.3 of Relax NG Schema: value-date-time.
      */
-    public function testRFC6351ValueDateTimeWithDayHourMinuteSecond()
+    public function testRFC6351ValueDateTimeWithDayHourMinuteSecond(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1718,7 +1718,7 @@ public function testRFC6351ValueDateTimeWithDayHourMinuteSecond()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:---28T135301'."\n".
@@ -1729,10 +1729,10 @@ public function testRFC6351ValueDateTimeWithDayHourMinuteSecond()
     /**
      * Section 4.3.3 of Relax NG Schema: value-date-time.
      */
-    public function testRFC6351ValueDateTimeWithDayHourZ()
+    public function testRFC6351ValueDateTimeWithDayHourZ(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1742,7 +1742,7 @@ public function testRFC6351ValueDateTimeWithDayHourZ()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:---28T13Z'."\n".
@@ -1753,10 +1753,10 @@ public function testRFC6351ValueDateTimeWithDayHourZ()
     /**
      * Section 4.3.3 of Relax NG Schema: value-date-time.
      */
-    public function testRFC6351ValueDateTimeWithDayHourTZ()
+    public function testRFC6351ValueDateTimeWithDayHourTZ(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1766,7 +1766,7 @@ public function testRFC6351ValueDateTimeWithDayHourTZ()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:---28T13+1234'."\n".
@@ -1777,10 +1777,10 @@ public function testRFC6351ValueDateTimeWithDayHourTZ()
     /**
      * Property: SOURCE.
      */
-    public function testRFC6350Section6Part1Part3()
+    public function testRFC6350Section6Part1Part3(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1790,7 +1790,7 @@ public function testRFC6350Section6Part1Part3()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'SOURCE:ldap://ldap.example.com/cn=Babs%20Jensen\,%20o=Babsco\,%20c=US'."\n".
@@ -1801,10 +1801,10 @@ public function testRFC6350Section6Part1Part3()
     /**
      * Property: KIND.
      */
-    public function testRFC6350Section6Part1Part4()
+    public function testRFC6350Section6Part1Part4(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1814,7 +1814,7 @@ public function testRFC6350Section6Part1Part4()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'KIND:individual'."\n".
@@ -1825,10 +1825,10 @@ public function testRFC6350Section6Part1Part4()
     /**
      * Property: FN.
      */
-    public function testRFC6350Section6Part2Part1()
+    public function testRFC6350Section6Part2Part1(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1838,7 +1838,7 @@ public function testRFC6350Section6Part2Part1()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'FN:Mr. John Q. Public\, Esq.'."\n".
@@ -1849,10 +1849,10 @@ public function testRFC6350Section6Part2Part1()
     /**
      * Property: N.
      */
-    public function testRFC6350Section6Part2Part2()
+    public function testRFC6350Section6Part2Part2(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1866,7 +1866,7 @@ public function testRFC6350Section6Part2Part2()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'N:Stevenson;John;Philip\,Paul;Dr.;Jr.\,M.D.\,A.C.P.'."\n".
@@ -1877,10 +1877,10 @@ public function testRFC6350Section6Part2Part2()
     /**
      * Property: NICKNAME.
      */
-    public function testRFC6350Section6Part2Part3()
+    public function testRFC6350Section6Part2Part3(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1891,7 +1891,7 @@ public function testRFC6350Section6Part2Part3()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'NICKNAME:Jim,Jimmie'."\n".
@@ -1902,10 +1902,10 @@ public function testRFC6350Section6Part2Part3()
     /**
      * Property: PHOTO.
      */
-    public function testRFC6350Section6Part2Part4()
+    public function testRFC6350Section6Part2Part4(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1915,7 +1915,7 @@ public function testRFC6350Section6Part2Part4()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'PHOTO:http://www.example.com/pub/photos/jqpublic.gif'."\n".
@@ -1923,10 +1923,10 @@ public function testRFC6350Section6Part2Part4()
         );
     }
 
-    public function testRFC6350Section6Part2Part5()
+    public function testRFC6350Section6Part2Part5(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1936,7 +1936,7 @@ public function testRFC6350Section6Part2Part5()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'BDAY:19531015T231000Z'."\n".
@@ -1944,10 +1944,10 @@ public function testRFC6350Section6Part2Part5()
         );
     }
 
-    public function testRFC6350Section6Part2Part6()
+    public function testRFC6350Section6Part2Part6(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1957,7 +1957,7 @@ public function testRFC6350Section6Part2Part6()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'ANNIVERSARY:19960415'."\n".
@@ -1968,10 +1968,10 @@ public function testRFC6350Section6Part2Part6()
     /**
      * Property: GENDER.
      */
-    public function testRFC6350Section6Part2Part7()
+    public function testRFC6350Section6Part2Part7(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -1982,7 +1982,7 @@ public function testRFC6350Section6Part2Part7()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'GENDER:Jim;Jimmie'."\n".
@@ -1993,10 +1993,10 @@ public function testRFC6350Section6Part2Part7()
     /**
      * Property: ADR.
      */
-    public function testRFC6350Section6Part3Part1()
+    public function testRFC6350Section6Part3Part1(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2012,7 +2012,7 @@ public function testRFC6350Section6Part3Part1()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'ADR:;;123 Main Street;Any Town;CA;91921-1234;U.S.A.'."\n".
@@ -2023,7 +2023,7 @@ public function testRFC6350Section6Part3Part1()
     /**
      * Property: TEL.
      */
-    public function testRFC6350Section6Part4Part1()
+    public function testRFC6350Section6Part4Part1(): void
     {
         /*
          * Quoting RFC:
@@ -2035,8 +2035,8 @@ public function testRFC6350Section6Part4Part1()
          * So first, we test xCard/URI to vCard/URI.
          * Then, we test xCard/TEXT to vCard/TEXT to xCard/TEXT.
          */
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2051,15 +2051,15 @@ public function testRFC6350Section6Part4Part1()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'TEL;TYPE=home:tel:+33-01-23-45-67'."\n".
             'END:VCARD'."\n"
         );
 
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2074,7 +2074,7 @@ public function testRFC6350Section6Part4Part1()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'TEL;TYPE=home:tel:+33-01-23-45-67'."\n".
@@ -2085,10 +2085,10 @@ public function testRFC6350Section6Part4Part1()
     /**
      * Property: EMAIL.
      */
-    public function testRFC6350Section6Part4Part2()
+    public function testRFC6350Section6Part4Part2(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2103,7 +2103,7 @@ public function testRFC6350Section6Part4Part2()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'EMAIL;TYPE=work:jqpublic@xyz.example.com'."\n".
@@ -2114,10 +2114,10 @@ public function testRFC6350Section6Part4Part2()
     /**
      * Property: IMPP.
      */
-    public function testRFC6350Section6Part4Part3()
+    public function testRFC6350Section6Part4Part3(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2132,7 +2132,7 @@ public function testRFC6350Section6Part4Part3()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'IMPP;PREF=1:xmpp:alice@example.com'."\n".
@@ -2143,10 +2143,10 @@ public function testRFC6350Section6Part4Part3()
     /**
      * Property: LANG.
      */
-    public function testRFC6350Section6Part4Part4()
+    public function testRFC6350Section6Part4Part4(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2164,7 +2164,7 @@ public function testRFC6350Section6Part4Part4()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'LANG;TYPE=work;PREF=2:en'."\n".
@@ -2175,10 +2175,10 @@ public function testRFC6350Section6Part4Part4()
     /**
      * Property: TZ.
      */
-    public function testRFC6350Section6Part5Part1()
+    public function testRFC6350Section6Part5Part1(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2188,7 +2188,7 @@ public function testRFC6350Section6Part5Part1()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'TZ:Raleigh/North America'."\n".
@@ -2199,10 +2199,10 @@ public function testRFC6350Section6Part5Part1()
     /**
      * Property: GEO.
      */
-    public function testRFC6350Section6Part5Part2()
+    public function testRFC6350Section6Part5Part2(): void
     {
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2212,15 +2212,15 @@ public function testRFC6350Section6Part5Part2()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'GEO:geo:37.386013\,-122.082932'."\n".
             'END:VCARD'."\n"
         );
 
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2230,7 +2230,7 @@ public function testRFC6350Section6Part5Part2()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'GEO:geo:37.386013\,-122.082932'."\n".
@@ -2241,10 +2241,10 @@ public function testRFC6350Section6Part5Part2()
     /**
      * Property: TITLE.
      */
-    public function testRFC6350Section6Part6Part1()
+    public function testRFC6350Section6Part6Part1(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2254,7 +2254,7 @@ public function testRFC6350Section6Part6Part1()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'TITLE:Research Scientist'."\n".
@@ -2265,10 +2265,10 @@ public function testRFC6350Section6Part6Part1()
     /**
      * Property: ROLE.
      */
-    public function testRFC6350Section6Part6Part2()
+    public function testRFC6350Section6Part6Part2(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2278,7 +2278,7 @@ public function testRFC6350Section6Part6Part2()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'ROLE:Project Leader'."\n".
@@ -2289,10 +2289,10 @@ public function testRFC6350Section6Part6Part2()
     /**
      * Property: LOGO.
      */
-    public function testRFC6350Section6Part6Part3()
+    public function testRFC6350Section6Part6Part3(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2302,7 +2302,7 @@ public function testRFC6350Section6Part6Part3()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'LOGO:http://www.example.com/pub/logos/abccorp.jpg'."\n".
@@ -2313,10 +2313,10 @@ public function testRFC6350Section6Part6Part3()
     /**
      * Property: ORG.
      */
-    public function testRFC6350Section6Part6Part4()
+    public function testRFC6350Section6Part6Part4(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2328,7 +2328,7 @@ public function testRFC6350Section6Part6Part4()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'ORG:ABC\, Inc.;North American Division;Marketing'."\n".
@@ -2339,10 +2339,10 @@ public function testRFC6350Section6Part6Part4()
     /**
      * Property: MEMBER.
      */
-    public function testRFC6350Section6Part6Part5()
+    public function testRFC6350Section6Part6Part5(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2352,15 +2352,15 @@ public function testRFC6350Section6Part6Part5()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'MEMBER:urn:uuid:03a0e51f-d1aa-4385-8a53-e29025acd8af'."\n".
             'END:VCARD'."\n"
         );
 
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2379,7 +2379,7 @@ public function testRFC6350Section6Part6Part5()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'MEMBER:mailto:subscriber1@example.com'."\n".
@@ -2393,10 +2393,10 @@ public function testRFC6350Section6Part6Part5()
     /**
      * Property: RELATED.
      */
-    public function testRFC6350Section6Part6Part6()
+    public function testRFC6350Section6Part6Part6(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2411,7 +2411,7 @@ public function testRFC6350Section6Part6Part6()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'RELATED;TYPE=friend:urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6'."\n".
@@ -2422,10 +2422,10 @@ public function testRFC6350Section6Part6Part6()
     /**
      * Property: CATEGORIES.
      */
-    public function testRFC6350Section6Part7Part1()
+    public function testRFC6350Section6Part7Part1(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2438,7 +2438,7 @@ public function testRFC6350Section6Part7Part1()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'CATEGORIES:INTERNET,IETF,INDUSTRY,INFORMATION TECHNOLOGY'."\n".
@@ -2449,10 +2449,10 @@ public function testRFC6350Section6Part7Part1()
     /**
      * Property: NOTE.
      */
-    public function testRFC6350Section6Part7Part2()
+    public function testRFC6350Section6Part7Part2(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2462,7 +2462,7 @@ public function testRFC6350Section6Part7Part2()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'NOTE:Foo\, bar'."\n".
@@ -2473,10 +2473,10 @@ public function testRFC6350Section6Part7Part2()
     /**
      * Property: PRODID.
      */
-    public function testRFC6350Section6Part7Part3()
+    public function testRFC6350Section6Part7Part3(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2486,7 +2486,7 @@ public function testRFC6350Section6Part7Part3()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'PRODID:-//ONLINE DIRECTORY//NONSGML Version 1//EN'."\n".
@@ -2494,10 +2494,10 @@ public function testRFC6350Section6Part7Part3()
         );
     }
 
-    public function testRFC6350Section6Part7Part4()
+    public function testRFC6350Section6Part7Part4(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2507,7 +2507,7 @@ public function testRFC6350Section6Part7Part4()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'REV:19951031T222710Z'."\n".
@@ -2518,10 +2518,10 @@ public function testRFC6350Section6Part7Part4()
     /**
      * Property: SOUND.
      */
-    public function testRFC6350Section6Part7Part5()
+    public function testRFC6350Section6Part7Part5(): void
     {
-        $this->assertXMLEqualsToMimeDir(
-<<<XML
+        self::assertXMLEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2531,15 +2531,15 @@ public function testRFC6350Section6Part7Part5()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'SOUND:CID:JOHNQPUBLIC.part8.19960229T080000.xyzMail@example.com'."\n".
             'END:VCARD'."\n"
         );
 
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2549,7 +2549,7 @@ public function testRFC6350Section6Part7Part5()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'SOUND:CID:JOHNQPUBLIC.part8.19960229T080000.xyzMail@example.com'."\n".
@@ -2560,10 +2560,10 @@ public function testRFC6350Section6Part7Part5()
     /**
      * Property: UID.
      */
-    public function testRFC6350Section6Part7Part6()
+    public function testRFC6350Section6Part7Part6(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2573,7 +2573,7 @@ public function testRFC6350Section6Part7Part6()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'UID:urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6'."\n".
@@ -2584,10 +2584,10 @@ public function testRFC6350Section6Part7Part6()
     /**
      * Property: CLIENTPIDMAP.
      */
-    public function testRFC6350Section6Part7Part7()
+    public function testRFC6350Section6Part7Part7(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2598,7 +2598,7 @@ public function testRFC6350Section6Part7Part7()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'CLIENTPIDMAP:1;urn:uuid:3df403f4-5924-4bb7-b077-3c711d9eb34b'."\n".
@@ -2609,10 +2609,10 @@ public function testRFC6350Section6Part7Part7()
     /**
      * Property: URL.
      */
-    public function testRFC6350Section6Part7Part8()
+    public function testRFC6350Section6Part7Part8(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2622,7 +2622,7 @@ public function testRFC6350Section6Part7Part8()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'URL:http://example.org/restaurant.french/~chezchic.html'."\n".
@@ -2633,16 +2633,16 @@ public function testRFC6350Section6Part7Part8()
     /**
      * Property: VERSION.
      */
-    public function testRFC6350Section6Part7Part9()
+    public function testRFC6350Section6Part7Part9(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard/>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'END:VCARD'."\n"
@@ -2652,10 +2652,10 @@ public function testRFC6350Section6Part7Part9()
     /**
      * Property: KEY.
      */
-    public function testRFC6350Section6Part8Part1()
+    public function testRFC6350Section6Part8Part1(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2670,7 +2670,7 @@ public function testRFC6350Section6Part8Part1()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'KEY;MEDIATYPE=application/pgp-keys:ftp://example.com/keys/jdoe'."\n".
@@ -2681,10 +2681,10 @@ public function testRFC6350Section6Part8Part1()
     /**
      * Property: FBURL.
      */
-    public function testRFC6350Section6Part9Part1()
+    public function testRFC6350Section6Part9Part1(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2699,7 +2699,7 @@ public function testRFC6350Section6Part9Part1()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'FBURL;PREF=1:http://www.example.com/busy/janedoe'."\n".
@@ -2710,10 +2710,10 @@ public function testRFC6350Section6Part9Part1()
     /**
      * Property: CALADRURI.
      */
-    public function testRFC6350Section6Part9Part2()
+    public function testRFC6350Section6Part9Part2(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2723,7 +2723,7 @@ public function testRFC6350Section6Part9Part2()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'CALADRURI:http://example.com/calendar/jdoe'."\n".
@@ -2734,10 +2734,10 @@ public function testRFC6350Section6Part9Part2()
     /**
      * Property: CALURI.
      */
-    public function testRFC6350Section6Part9Part3()
+    public function testRFC6350Section6Part9Part3(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2752,7 +2752,7 @@ public function testRFC6350Section6Part9Part3()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'CALURI;PREF=1:http://cal.example.com/calA'."\n".
@@ -2763,10 +2763,10 @@ public function testRFC6350Section6Part9Part3()
     /**
      * Property: CAPURI.
      */
-    public function testRFC6350SectionAPart3()
+    public function testRFC6350SectionAPart3(): void
     {
-        $this->assertXMLReflexivelyEqualsToMimeDir(
-<<<XML
+        self::assertXMLReflexivelyEqualsToMimeDir(
+            <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
 <vcards xmlns="urn:ietf:params:xml:ns:vcard-4.0">
  <vcard>
@@ -2776,7 +2776,7 @@ public function testRFC6350SectionAPart3()
  </vcard>
 </vcards>
 XML
-,
+            ,
             'BEGIN:VCARD'."\n".
             'VERSION:4.0'."\n".
             'CAPURI:http://cap.example.com/capA'."\n".
@@ -2788,21 +2788,21 @@ public function testRFC6350SectionAPart3()
      * Check this equality:
      *     XML -> object model -> MIME Dir.
      */
-    protected function assertXMLEqualsToMimeDir($xml, $mimedir)
+    protected function assertXMLEqualsToMimeDir(string $xml, string $mimedir): void
     {
         $component = VObject\Reader::readXML($xml);
-        $this->assertVObjectEqualsVObject($mimedir, $component);
+        self::assertVObjectEqualsVObject($mimedir, $component);
     }
 
     /**
      * Check this (reflexive) equality:
      *     XML -> object model -> MIME Dir -> object model -> XML.
      */
-    protected function assertXMLReflexivelyEqualsToMimeDir($xml, $mimedir)
+    protected function assertXMLReflexivelyEqualsToMimeDir(string $xml, string $mimedir): void
     {
-        $this->assertXMLEqualsToMimeDir($xml, $mimedir);
+        self::assertXMLEqualsToMimeDir($xml, $mimedir);
 
         $component = VObject\Reader::read($mimedir);
-        $this->assertXmlStringEqualsXmlString($xml, VObject\Writer::writeXML($component));
+        self::assertXmlStringEqualsXmlString($xml, VObject\Writer::writeXML($component));
     }
 }
diff --git a/tests/VObject/Property/BinaryTest.php b/tests/VObject/Property/BinaryTest.php
index b1c2dada7..8d2736573 100644
--- a/tests/VObject/Property/BinaryTest.php
+++ b/tests/VObject/Property/BinaryTest.php
@@ -7,7 +7,7 @@
 
 class BinaryTest extends TestCase
 {
-    public function testMimeDir()
+    public function testMimeDir(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $vcard = new VObject\Component\VCard(['VERSION' => '3.0']);
diff --git a/tests/VObject/Property/BooleanTest.php b/tests/VObject/Property/BooleanTest.php
index ad2ccbcd7..82684dd71 100644
--- a/tests/VObject/Property/BooleanTest.php
+++ b/tests/VObject/Property/BooleanTest.php
@@ -7,15 +7,18 @@
 
 class BooleanTest extends TestCase
 {
-    public function testMimeDir()
+    /**
+     * @throws VObject\ParseException
+     */
+    public function testMimeDir(): void
     {
         $input = "BEGIN:VCARD\r\nX-AWESOME;VALUE=BOOLEAN:TRUE\r\nX-SUCKS;VALUE=BOOLEAN:FALSE\r\nEND:VCARD\r\n";
 
         $vcard = VObject\Reader::read($input);
-        $this->assertTrue($vcard->{'X-AWESOME'}->getValue());
-        $this->assertFalse($vcard->{'X-SUCKS'}->getValue());
+        self::assertTrue($vcard->{'X-AWESOME'}->getValue());
+        self::assertFalse($vcard->{'X-SUCKS'}->getValue());
 
-        $this->assertEquals('BOOLEAN', $vcard->{'X-AWESOME'}->getValueType());
-        $this->assertEquals($input, $vcard->serialize());
+        self::assertEquals('BOOLEAN', $vcard->{'X-AWESOME'}->getValueType());
+        self::assertEquals($input, $vcard->serialize());
     }
 }
diff --git a/tests/VObject/Property/CompoundTest.php b/tests/VObject/Property/CompoundTest.php
index bfa1ed64b..073d9627a 100644
--- a/tests/VObject/Property/CompoundTest.php
+++ b/tests/VObject/Property/CompoundTest.php
@@ -7,7 +7,7 @@
 
 class CompoundTest extends TestCase
 {
-    public function testSetParts()
+    public function testSetParts(): void
     {
         $arr = [
             'ABC, Inc.',
@@ -19,13 +19,13 @@ public function testSetParts()
         $elem = $vcard->createProperty('ORG');
         $elem->setParts($arr);
 
-        $this->assertEquals('ABC\, Inc.;North American Division;Marketing\;Sales', $elem->getValue());
-        $this->assertEquals(3, count($elem->getParts()));
+        self::assertEquals('ABC\, Inc.;North American Division;Marketing\;Sales', $elem->getValue());
+        self::assertCount(3, $elem->getParts());
         $parts = $elem->getParts();
-        $this->assertEquals('Marketing;Sales', $parts[2]);
+        self::assertEquals('Marketing;Sales', $parts[2]);
     }
 
-    public function testGetParts()
+    public function testGetParts(): void
     {
         $str = 'ABC\, Inc.;North American Division;Marketing\;Sales';
 
@@ -33,16 +33,16 @@ public function testGetParts()
         $elem = $vcard->createProperty('ORG');
         $elem->setRawMimeDirValue($str);
 
-        $this->assertEquals(3, count($elem->getParts()));
+        self::assertCount(3, $elem->getParts());
         $parts = $elem->getParts();
-        $this->assertEquals('Marketing;Sales', $parts[2]);
+        self::assertEquals('Marketing;Sales', $parts[2]);
     }
 
-    public function testGetPartsNull()
+    public function testGetPartsNull(): void
     {
         $vcard = new VCard();
         $elem = $vcard->createProperty('ORG', null);
 
-        $this->assertEquals(0, count($elem->getParts()));
+        self::assertCount(0, $elem->getParts());
     }
 }
diff --git a/tests/VObject/Property/FloatTest.php b/tests/VObject/Property/FloatTest.php
index 0ba02470e..b5fee5d75 100644
--- a/tests/VObject/Property/FloatTest.php
+++ b/tests/VObject/Property/FloatTest.php
@@ -7,21 +7,21 @@
 
 class FloatTest extends TestCase
 {
-    public function testMimeDir()
+    public function testMimeDir(): void
     {
         $input = "BEGIN:VCARD\r\nVERSION:4.0\r\nX-FLOAT;VALUE=FLOAT:0.234;1.245\r\nEND:VCARD\r\n";
         $mimeDir = new VObject\Parser\MimeDir($input);
 
         $result = $mimeDir->parse($input);
 
-        $this->assertInstanceOf(FloatValue::class, $result->{'X-FLOAT'});
+        self::assertInstanceOf(FloatValue::class, $result->{'X-FLOAT'});
 
-        $this->assertEquals([
+        self::assertEquals([
             0.234,
             1.245,
         ], $result->{'X-FLOAT'}->getParts());
 
-        $this->assertEquals(
+        self::assertEquals(
             $input,
             $result->serialize()
         );
diff --git a/tests/VObject/Property/ICalendar/CalAddressTest.php b/tests/VObject/Property/ICalendar/CalAddressTest.php
index a907daf5c..b774f4fbc 100644
--- a/tests/VObject/Property/ICalendar/CalAddressTest.php
+++ b/tests/VObject/Property/ICalendar/CalAddressTest.php
@@ -9,22 +9,24 @@ class CalAddressTest extends TestCase
     /**
      * @dataProvider values
      */
-    public function testGetNormalizedValue($expected, $input)
+    public function testGetNormalizedValue(string $expected, string $input): void
     {
         $vobj = new \Sabre\VObject\Component\VCalendar();
         $property = $vobj->add('ATTENDEE', $input);
 
-        $this->assertEquals(
+        self::assertEquals(
             $expected,
             $property->getNormalizedValue()
         );
     }
 
-    public function values()
+    public function values(): array
     {
         return [
             ['mailto:a@b.com', 'mailto:a@b.com'],
             ['mailto:a@b.com', 'MAILTO:a@b.com'],
+            ['mailto:a@b.com', 'mailto:A@B.COM'],
+            ['mailto:a@b.com', 'MAILTO:A@B.COM'],
             ['/foo/bar', '/foo/bar'],
         ];
     }
diff --git a/tests/VObject/Property/ICalendar/DateTimeTest.php b/tests/VObject/Property/ICalendar/DateTimeTest.php
index aa584dba5..0da557b93 100644
--- a/tests/VObject/Property/ICalendar/DateTimeTest.php
+++ b/tests/VObject/Property/ICalendar/DateTimeTest.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Property\ICalendar;
 
-use InvalidArgumentException;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\InvalidDataException;
@@ -16,7 +15,7 @@ public function setUp(): void
         $this->vcal = new VCalendar();
     }
 
-    public function testSetDateTime()
+    public function testSetDateTime(): void
     {
         $tz = new \DateTimeZone('Europe/Amsterdam');
         $dt = new \DateTime('1985-07-04 01:30:00', $tz);
@@ -25,29 +24,29 @@ public function testSetDateTime()
         $elem = $this->vcal->createProperty('DTSTART');
         $elem->setDateTime($dt);
 
-        $this->assertEquals('19850704T013000', (string) $elem);
-        $this->assertEquals('Europe/Amsterdam', (string) $elem['TZID']);
-        $this->assertNull($elem['VALUE']);
+        self::assertEquals('19850704T013000', (string) $elem);
+        self::assertEquals('Europe/Amsterdam', (string) $elem['TZID']);
+        self::assertNull($elem['VALUE']);
 
-        $this->assertTrue($elem->hasTime());
+        self::assertTrue($elem->hasTime());
     }
 
-    public function testSetDateTimeLOCAL()
+    public function testSetDateTimeLOCAL(): void
     {
         $tz = new \DateTimeZone('Europe/Amsterdam');
         $dt = new \DateTime('1985-07-04 01:30:00', $tz);
         $dt->setTimeZone($tz);
 
         $elem = $this->vcal->createProperty('DTSTART');
-        $elem->setDateTime($dt, $isFloating = true);
+        $elem->setDateTime($dt, true);
 
-        $this->assertEquals('19850704T013000', (string) $elem);
-        $this->assertNull($elem['TZID']);
+        self::assertEquals('19850704T013000', (string) $elem);
+        self::assertNull($elem['TZID']);
 
-        $this->assertTrue($elem->hasTime());
+        self::assertTrue($elem->hasTime());
     }
 
-    public function testSetDateTimeUTC()
+    public function testSetDateTimeUTC(): void
     {
         $tz = new \DateTimeZone('GMT');
         $dt = new \DateTime('1985-07-04 01:30:00', $tz);
@@ -56,13 +55,13 @@ public function testSetDateTimeUTC()
         $elem = $this->vcal->createProperty('DTSTART');
         $elem->setDateTime($dt);
 
-        $this->assertEquals('19850704T013000Z', (string) $elem);
-        $this->assertNull($elem['TZID']);
+        self::assertEquals('19850704T013000Z', (string) $elem);
+        self::assertNull($elem['TZID']);
 
-        $this->assertTrue($elem->hasTime());
+        self::assertTrue($elem->hasTime());
     }
 
-    public function testSetDateTimeFromUnixTimestamp()
+    public function testSetDateTimeFromUnixTimestamp(): void
     {
         // When initialized from a Unix timestamp, the timezone is set to "+00:00".
         $dt = new \DateTime('@489288600');
@@ -70,13 +69,13 @@ public function testSetDateTimeFromUnixTimestamp()
         $elem = $this->vcal->createProperty('DTSTART');
         $elem->setDateTime($dt);
 
-        $this->assertEquals('19850704T013000Z', (string) $elem);
-        $this->assertNull($elem['TZID']);
+        self::assertEquals('19850704T013000Z', (string) $elem);
+        self::assertNull($elem['TZID']);
 
-        $this->assertTrue($elem->hasTime());
+        self::assertTrue($elem->hasTime());
     }
 
-    public function testSetDateTimeLOCALTZ()
+    public function testSetDateTimeLOCALTZ(): void
     {
         $tz = new \DateTimeZone('Europe/Amsterdam');
         $dt = new \DateTime('1985-07-04 01:30:00', $tz);
@@ -85,13 +84,13 @@ public function testSetDateTimeLOCALTZ()
         $elem = $this->vcal->createProperty('DTSTART');
         $elem->setDateTime($dt);
 
-        $this->assertEquals('19850704T013000', (string) $elem);
-        $this->assertEquals('Europe/Amsterdam', (string) $elem['TZID']);
+        self::assertEquals('19850704T013000', (string) $elem);
+        self::assertEquals('Europe/Amsterdam', (string) $elem['TZID']);
 
-        $this->assertTrue($elem->hasTime());
+        self::assertTrue($elem->hasTime());
     }
 
-    public function testSetDateTimeDATE()
+    public function testSetDateTimeDATE(): void
     {
         $tz = new \DateTimeZone('Europe/Amsterdam');
         $dt = new \DateTime('1985-07-04 01:30:00', $tz);
@@ -101,14 +100,14 @@ public function testSetDateTimeDATE()
         $elem['VALUE'] = 'DATE';
         $elem->setDateTime($dt);
 
-        $this->assertEquals('19850704', (string) $elem);
-        $this->assertNull($elem['TZID']);
-        $this->assertEquals('DATE', (string) $elem['VALUE']);
+        self::assertEquals('19850704', (string) $elem);
+        self::assertNull($elem['TZID']);
+        self::assertEquals('DATE', (string) $elem['VALUE']);
 
-        $this->assertFalse($elem->hasTime());
+        self::assertFalse($elem->hasTime());
     }
 
-    public function testSetValue()
+    public function testSetValue(): void
     {
         $tz = new \DateTimeZone('Europe/Amsterdam');
         $dt = new \DateTime('1985-07-04 01:30:00', $tz);
@@ -117,14 +116,14 @@ public function testSetValue()
         $elem = $this->vcal->createProperty('DTSTART');
         $elem->setValue($dt);
 
-        $this->assertEquals('19850704T013000', (string) $elem);
-        $this->assertEquals('Europe/Amsterdam', (string) $elem['TZID']);
-        $this->assertNull($elem['VALUE']);
+        self::assertEquals('19850704T013000', (string) $elem);
+        self::assertEquals('Europe/Amsterdam', (string) $elem['TZID']);
+        self::assertNull($elem['VALUE']);
 
-        $this->assertTrue($elem->hasTime());
+        self::assertTrue($elem->hasTime());
     }
 
-    public function testSetValueArray()
+    public function testSetValueArray(): void
     {
         $tz = new \DateTimeZone('Europe/Amsterdam');
         $dt1 = new \DateTime('1985-07-04 01:30:00', $tz);
@@ -135,14 +134,14 @@ public function testSetValueArray()
         $elem = $this->vcal->createProperty('DTSTART');
         $elem->setValue([$dt1, $dt2]);
 
-        $this->assertEquals('19850704T013000,19850704T023000', (string) $elem);
-        $this->assertEquals('Europe/Amsterdam', (string) $elem['TZID']);
-        $this->assertNull($elem['VALUE']);
+        self::assertEquals('19850704T013000,19850704T023000', (string) $elem);
+        self::assertEquals('Europe/Amsterdam', (string) $elem['TZID']);
+        self::assertNull($elem['VALUE']);
 
-        $this->assertTrue($elem->hasTime());
+        self::assertTrue($elem->hasTime());
     }
 
-    public function testSetParts()
+    public function testSetParts(): void
     {
         $tz = new \DateTimeZone('Europe/Amsterdam');
         $dt1 = new \DateTime('1985-07-04 01:30:00', $tz);
@@ -153,14 +152,14 @@ public function testSetParts()
         $elem = $this->vcal->createProperty('DTSTART');
         $elem->setParts([$dt1, $dt2]);
 
-        $this->assertEquals('19850704T013000,19850704T023000', (string) $elem);
-        $this->assertEquals('Europe/Amsterdam', (string) $elem['TZID']);
-        $this->assertNull($elem['VALUE']);
+        self::assertEquals('19850704T013000,19850704T023000', (string) $elem);
+        self::assertEquals('Europe/Amsterdam', (string) $elem['TZID']);
+        self::assertNull($elem['VALUE']);
 
-        $this->assertTrue($elem->hasTime());
+        self::assertTrue($elem->hasTime());
     }
 
-    public function testSetPartsStrings()
+    public function testSetPartsStrings(): void
     {
         $dt1 = '19850704T013000Z';
         $dt2 = '19850704T023000Z';
@@ -168,13 +167,13 @@ public function testSetPartsStrings()
         $elem = $this->vcal->createProperty('DTSTART');
         $elem->setParts([$dt1, $dt2]);
 
-        $this->assertEquals('19850704T013000Z,19850704T023000Z', (string) $elem);
-        $this->assertNull($elem['VALUE']);
+        self::assertEquals('19850704T013000Z,19850704T023000Z', (string) $elem);
+        self::assertNull($elem['VALUE']);
 
-        $this->assertTrue($elem->hasTime());
+        self::assertTrue($elem->hasTime());
     }
 
-    public function testGetDateTimeCached()
+    public function testGetDateTimeCached(): void
     {
         $tz = new \DateTimeZone('Europe/Amsterdam');
         $dt = new \DateTimeImmutable('1985-07-04 01:30:00', $tz);
@@ -183,27 +182,27 @@ public function testGetDateTimeCached()
         $elem = $this->vcal->createProperty('DTSTART');
         $elem->setDateTime($dt);
 
-        $this->assertEquals($elem->getDateTime(), $dt);
+        self::assertEquals($elem->getDateTime(), $dt);
     }
 
-    public function testGetDateTimeDateNULL()
+    public function testGetDateTimeDateNULL(): void
     {
         $elem = $this->vcal->createProperty('DTSTART');
         $dt = $elem->getDateTime();
 
-        $this->assertNull($dt);
+        self::assertNull($dt);
     }
 
-    public function testGetDateTimeDateDATE()
+    public function testGetDateTimeDateDATE(): void
     {
         $elem = $this->vcal->createProperty('DTSTART', '19850704');
         $dt = $elem->getDateTime();
 
-        $this->assertInstanceOf('DateTimeImmutable', $dt);
-        $this->assertEquals('1985-07-04 00:00:00', $dt->format('Y-m-d H:i:s'));
+        self::assertInstanceOf('DateTimeImmutable', $dt);
+        self::assertEquals('1985-07-04 00:00:00', $dt->format('Y-m-d H:i:s'));
     }
 
-    public function testGetDateTimeDateDATEReferenceTimeZone()
+    public function testGetDateTimeDateDATEReferenceTimeZone(): void
     {
         $elem = $this->vcal->createProperty('DTSTART', '19850704');
 
@@ -211,20 +210,20 @@ public function testGetDateTimeDateDATEReferenceTimeZone()
         $dt = $elem->getDateTime($tz);
         $dt = $dt->setTimeZone(new \DateTimeZone('UTC'));
 
-        $this->assertInstanceOf('DateTimeImmutable', $dt);
-        $this->assertEquals('1985-07-04 04:00:00', $dt->format('Y-m-d H:i:s'));
+        self::assertInstanceOf('DateTimeImmutable', $dt);
+        self::assertEquals('1985-07-04 04:00:00', $dt->format('Y-m-d H:i:s'));
     }
 
-    public function testGetDateTimeDateFloating()
+    public function testGetDateTimeDateFloating(): void
     {
         $elem = $this->vcal->createProperty('DTSTART', '19850704T013000');
         $dt = $elem->getDateTime();
 
-        $this->assertInstanceOf('DateTimeImmutable', $dt);
-        $this->assertEquals('1985-07-04 01:30:00', $dt->format('Y-m-d H:i:s'));
+        self::assertInstanceOf('DateTimeImmutable', $dt);
+        self::assertEquals('1985-07-04 01:30:00', $dt->format('Y-m-d H:i:s'));
     }
 
-    public function testGetDateTimeDateFloatingReferenceTimeZone()
+    public function testGetDateTimeDateFloatingReferenceTimeZone(): void
     {
         $elem = $this->vcal->createProperty('DTSTART', '19850704T013000');
 
@@ -232,40 +231,40 @@ public function testGetDateTimeDateFloatingReferenceTimeZone()
         $dt = $elem->getDateTime($tz);
         $dt = $dt->setTimeZone(new \DateTimeZone('UTC'));
 
-        $this->assertInstanceOf('DateTimeInterface', $dt);
-        $this->assertEquals('1985-07-04 05:30:00', $dt->format('Y-m-d H:i:s'));
+        self::assertInstanceOf('DateTimeInterface', $dt);
+        self::assertEquals('1985-07-04 05:30:00', $dt->format('Y-m-d H:i:s'));
     }
 
-    public function testGetDateTimeDateUTC()
+    public function testGetDateTimeDateUTC(): void
     {
         $elem = $this->vcal->createProperty('DTSTART', '19850704T013000Z');
         $dt = $elem->getDateTime();
 
-        $this->assertInstanceOf('DateTimeImmutable', $dt);
-        $this->assertEquals('1985-07-04 01:30:00', $dt->format('Y-m-d H:i:s'));
-        $this->assertEquals('UTC', $dt->getTimeZone()->getName());
+        self::assertInstanceOf('DateTimeImmutable', $dt);
+        self::assertEquals('1985-07-04 01:30:00', $dt->format('Y-m-d H:i:s'));
+        self::assertEquals('UTC', $dt->getTimeZone()->getName());
     }
 
-    public function testGetDateTimeDateLOCALTZ()
+    public function testGetDateTimeDateLOCALTZ(): void
     {
         $elem = $this->vcal->createProperty('DTSTART', '19850704T013000');
         $elem['TZID'] = 'Europe/Amsterdam';
 
         $dt = $elem->getDateTime();
 
-        $this->assertInstanceOf('DateTimeImmutable', $dt);
-        $this->assertEquals('1985-07-04 01:30:00', $dt->format('Y-m-d H:i:s'));
-        $this->assertEquals('Europe/Amsterdam', $dt->getTimeZone()->getName());
+        self::assertInstanceOf('DateTimeImmutable', $dt);
+        self::assertEquals('1985-07-04 01:30:00', $dt->format('Y-m-d H:i:s'));
+        self::assertEquals('Europe/Amsterdam', $dt->getTimeZone()->getName());
     }
 
-    public function testGetDateTimeDateInvalid()
+    public function testGetDateTimeDateInvalid(): void
     {
         $this->expectException(InvalidDataException::class);
         $elem = $this->vcal->createProperty('DTSTART', 'bla');
-        $dt = $elem->getDateTime();
+        $elem->getDateTime();
     }
 
-    public function testGetDateTimeWeirdTZ()
+    public function testGetDateTimeWeirdTZ(): void
     {
         $elem = $this->vcal->createProperty('DTSTART', '19850704T013000');
         $elem['TZID'] = '/freeassociation.sourceforge.net/Tzfile/Europe/Amsterdam';
@@ -282,12 +281,12 @@ public function testGetDateTimeWeirdTZ()
 
         $dt = $elem->getDateTime();
 
-        $this->assertInstanceOf('DateTimeImmutable', $dt);
-        $this->assertEquals('1985-07-04 01:30:00', $dt->format('Y-m-d H:i:s'));
-        $this->assertEquals('Europe/Amsterdam', $dt->getTimeZone()->getName());
+        self::assertInstanceOf('DateTimeImmutable', $dt);
+        self::assertEquals('1985-07-04 01:30:00', $dt->format('Y-m-d H:i:s'));
+        self::assertEquals('Europe/Amsterdam', $dt->getTimeZone()->getName());
     }
 
-    public function testGetDateTimeBadTimeZone()
+    public function testGetDateTimeBadTimeZone(): void
     {
         $default = date_default_timezone_get();
         date_default_timezone_set('Canada/Eastern');
@@ -306,31 +305,31 @@ public function testGetDateTimeBadTimeZone()
         $this->vcal->add($timezone);
 
         date_default_timezone_set($default);
-        $this->expectException(InvalidArgumentException::class);
+        $this->expectException(\InvalidArgumentException::class);
         $this->expectExceptionMessage('We were unable to determine the correct PHP timezone for tzid: Moon');
         $elem->getDateTime();
     }
 
-    public function testUpdateValueParameter()
+    public function testUpdateValueParameter(): void
     {
         $dtStart = $this->vcal->createProperty('DTSTART', new \DateTime('2013-06-07 15:05:00'));
         $dtStart['VALUE'] = 'DATE';
 
-        $this->assertEquals("DTSTART;VALUE=DATE:20130607\r\n", $dtStart->serialize());
+        self::assertEquals("DTSTART;VALUE=DATE:20130607\r\n", $dtStart->serialize());
     }
 
-    public function testValidate()
+    public function testValidate(): void
     {
         $exDate = $this->vcal->createProperty('EXDATE', '-00011130T143000Z');
         $messages = $exDate->validate();
-        $this->assertEquals(1, count($messages));
-        $this->assertEquals(3, $messages[0]['level']);
+        self::assertCount(1, $messages);
+        self::assertEquals(3, $messages[0]['level']);
     }
 
     /**
      * This issue was discovered on the sabredav mailing list.
      */
-    public function testCreateDatePropertyThroughAdd()
+    public function testCreateDatePropertyThroughAdd(): void
     {
         $vcal = new VCalendar();
         $vevent = $vcal->add('VEVENT');
@@ -341,6 +340,6 @@ public function testCreateDatePropertyThroughAdd()
             ['VALUE' => 'DATE']
         );
 
-        $this->assertEquals("DTSTART;VALUE=DATE:20140307\r\n", $dtstart->serialize());
+        self::assertEquals("DTSTART;VALUE=DATE:20140307\r\n", $dtstart->serialize());
     }
 }
diff --git a/tests/VObject/Property/ICalendar/DurationTest.php b/tests/VObject/Property/ICalendar/DurationTest.php
index 2003ad6d2..044f86279 100644
--- a/tests/VObject/Property/ICalendar/DurationTest.php
+++ b/tests/VObject/Property/ICalendar/DurationTest.php
@@ -7,12 +7,12 @@
 
 class DurationTest extends TestCase
 {
-    public function testGetDateInterval()
+    public function testGetDateInterval(): void
     {
         $vcal = new VCalendar();
         $event = $vcal->add('VEVENT', ['DURATION' => ['PT1H']]);
 
-        $this->assertEquals(
+        self::assertEquals(
             new \DateInterval('PT1H'),
             $event->{'DURATION'}->getDateInterval()
         );
diff --git a/tests/VObject/Property/ICalendar/RecurTest.php b/tests/VObject/Property/ICalendar/RecurTest.php
index 3902a6e13..b2750f03b 100644
--- a/tests/VObject/Property/ICalendar/RecurTest.php
+++ b/tests/VObject/Property/ICalendar/RecurTest.php
@@ -11,20 +11,20 @@ class RecurTest extends TestCase
 {
     use \Sabre\VObject\PHPUnitAssertions;
 
-    public function testParts()
+    public function testParts(): void
     {
         $vcal = new VCalendar();
         $recur = $vcal->add('RRULE', 'FREQ=Daily');
 
-        $this->assertInstanceOf(Recur::class, $recur);
+        self::assertInstanceOf(Recur::class, $recur);
 
-        $this->assertEquals(['FREQ' => 'DAILY'], $recur->getParts());
+        self::assertEquals(['FREQ' => 'DAILY'], $recur->getParts());
         $recur->setParts(['freq' => 'MONTHLY']);
 
-        $this->assertEquals(['FREQ' => 'MONTHLY'], $recur->getParts());
+        self::assertEquals(['FREQ' => 'MONTHLY'], $recur->getParts());
     }
 
-    public function testSetValueBadVal()
+    public function testSetValueBadVal(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $vcal = new VCalendar();
@@ -32,15 +32,15 @@ public function testSetValueBadVal()
         $recur->setValue(new \Exception());
     }
 
-    public function testSetValueWithCount()
+    public function testSetValueWithCount(): void
     {
         $vcal = new VCalendar();
         $recur = $vcal->add('RRULE', 'FREQ=Daily');
         $recur->setValue(['COUNT' => 3]);
-        $this->assertEquals($recur->getParts()['COUNT'], 3);
+        self::assertEquals(3, $recur->getParts()['COUNT']);
     }
 
-    public function testGetJSONWithCount()
+    public function testGetJSONWithCount(): void
     {
         $input = 'BEGIN:VCALENDAR
 BEGIN:VEVENT
@@ -58,23 +58,23 @@ public function testGetJSONWithCount()
         $vcal = Reader::read($input);
         $rrule = $vcal->VEVENT->RRULE;
         $count = $rrule->getJsonValue()[0]['count'];
-        $this->assertTrue(is_int($count));
-        $this->assertEquals(3, $count);
+        self::assertTrue(is_int($count));
+        self::assertEquals(3, $count);
     }
 
-    public function testSetSubParts()
+    public function testSetSubParts(): void
     {
         $vcal = new VCalendar();
         $recur = $vcal->add('RRULE', ['FREQ' => 'DAILY', 'BYDAY' => 'mo,tu', 'BYMONTH' => [0, 1]]);
 
-        $this->assertEquals([
+        self::assertEquals([
             'FREQ' => 'DAILY',
             'BYDAY' => ['MO', 'TU'],
             'BYMONTH' => [0, 1],
         ], $recur->getParts());
     }
 
-    public function testGetJSONWithUntil()
+    public function testGetJSONWithUntil(): void
     {
         $input = 'BEGIN:VCALENDAR
 BEGIN:VEVENT
@@ -92,10 +92,10 @@ public function testGetJSONWithUntil()
         $vcal = Reader::read($input);
         $rrule = $vcal->VEVENT->RRULE;
         $untilJsonString = $rrule->getJsonValue()[0]['until'];
-        $this->assertEquals('2016-03-05T23:00:00Z', $untilJsonString);
+        self::assertEquals('2016-03-05T23:00:00Z', $untilJsonString);
     }
 
-    public function testValidateStripEmpties()
+    public function testValidateStripEmpties(): void
     {
         $input = 'BEGIN:VCALENDAR
 VERSION:2.0
@@ -114,13 +114,13 @@ public function testValidateStripEmpties()
 ';
 
         $vcal = Reader::read($input);
-        $this->assertEquals(
+        self::assertCount(
             1,
-            count($vcal->validate())
+            $vcal->validate()
         );
-        $this->assertEquals(
+        self::assertCount(
             1,
-            count($vcal->validate($vcal::REPAIR))
+            $vcal->validate($vcal::REPAIR)
         );
 
         $expected = 'BEGIN:VCALENDAR
@@ -139,13 +139,13 @@ public function testValidateStripEmpties()
 END:VCALENDAR
 ';
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $vcal
         );
     }
 
-    public function testValidateStripNoFreq()
+    public function testValidateStripNoFreq(): void
     {
         $input = 'BEGIN:VCALENDAR
 VERSION:2.0
@@ -164,13 +164,13 @@ public function testValidateStripNoFreq()
 ';
 
         $vcal = Reader::read($input);
-        $this->assertEquals(
+        self::assertCount(
             1,
-            count($vcal->validate())
+            $vcal->validate()
         );
-        $this->assertEquals(
+        self::assertCount(
             1,
-            count($vcal->validate($vcal::REPAIR))
+            $vcal->validate($vcal::REPAIR)
         );
 
         $expected = 'BEGIN:VCALENDAR
@@ -188,243 +188,243 @@ public function testValidateStripNoFreq()
 END:VCALENDAR
 ';
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $vcal
         );
     }
 
-    public function testValidateInvalidByMonthRruleWithRepair()
+    public function testValidateInvalidByMonthRruleWithRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=0');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(1, $result);
-        $this->assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
-        $this->assertEquals(1, $result[0]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24', $property->getValue());
+        self::assertCount(1, $result);
+        self::assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
+        self::assertEquals(1, $result[0]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24', $property->getValue());
     }
 
-    public function testValidateInvalidByMonthRruleWithoutRepair()
+    public function testValidateInvalidByMonthRruleWithoutRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=0');
         $result = $property->validate();
 
-        $this->assertCount(1, $result);
-        $this->assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
-        $this->assertEquals(3, $result[0]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=0', $property->getValue());
+        self::assertCount(1, $result);
+        self::assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
+        self::assertEquals(3, $result[0]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=0', $property->getValue());
     }
 
-    public function testValidateInvalidByMonthRruleWithRepair2()
+    public function testValidateInvalidByMonthRruleWithRepair2(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=bla');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(1, $result);
-        $this->assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
-        $this->assertEquals(1, $result[0]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24', $property->getValue());
+        self::assertCount(1, $result);
+        self::assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
+        self::assertEquals(1, $result[0]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24', $property->getValue());
     }
 
-    public function testValidateInvalidByMonthRruleWithoutRepair2()
+    public function testValidateInvalidByMonthRruleWithoutRepair2(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=bla');
         $result = $property->validate();
 
-        $this->assertCount(1, $result);
-        $this->assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
-        $this->assertEquals(3, $result[0]['level']);
+        self::assertCount(1, $result);
+        self::assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
+        self::assertEquals(3, $result[0]['level']);
         // Without repair the invalid BYMONTH is still there, but the value is changed to uppercase
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=BLA', $property->getValue());
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=BLA', $property->getValue());
     }
 
-    public function testValidateInvalidByMonthRruleValue14WithRepair()
+    public function testValidateInvalidByMonthRruleValue14WithRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=14');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(1, $result);
-        $this->assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
-        $this->assertEquals(1, $result[0]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24', $property->getValue());
+        self::assertCount(1, $result);
+        self::assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
+        self::assertEquals(1, $result[0]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24', $property->getValue());
     }
 
-    public function testValidateInvalidByMonthRruleMultipleWithRepair()
+    public function testValidateInvalidByMonthRruleMultipleWithRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=0,1,2,3,4,14');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(2, $result);
-        $this->assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
-        $this->assertEquals(1, $result[0]['level']);
-        $this->assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[1]['message']);
-        $this->assertEquals(1, $result[1]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=1,2,3,4', $property->getValue());
+        self::assertCount(2, $result);
+        self::assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
+        self::assertEquals(1, $result[0]['level']);
+        self::assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[1]['message']);
+        self::assertEquals(1, $result[1]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=1,2,3,4', $property->getValue());
     }
 
-    public function testValidateOneOfManyInvalidByMonthRruleWithRepair()
+    public function testValidateOneOfManyInvalidByMonthRruleWithRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=bla,3,foo');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(2, $result);
-        $this->assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
-        $this->assertEquals(1, $result[0]['level']);
-        $this->assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[1]['message']);
-        $this->assertEquals(1, $result[1]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=3', $property->getValue());
+        self::assertCount(2, $result);
+        self::assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[0]['message']);
+        self::assertEquals(1, $result[0]['level']);
+        self::assertEquals('BYMONTH in RRULE must have value(s) between 1 and 12!', $result[1]['message']);
+        self::assertEquals(1, $result[1]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=3', $property->getValue());
     }
 
-    public function testValidateValidByMonthRrule()
+    public function testValidateValidByMonthRrule(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=2,3');
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=2,3', $property->getValue());
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYMONTHDAY=24;BYMONTH=2,3', $property->getValue());
     }
 
     /**
      * test for issue #336.
      */
-    public function testValidateRruleBySecondZero()
+    public function testValidateRruleBySecondZero(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=DAILY;BYHOUR=10;BYMINUTE=30;BYSECOND=0;UNTIL=20150616T153000Z');
         $result = $property->validate(Node::REPAIR);
 
         // There should be 0 warnings and the value should be unchanged
-        $this->assertEmpty($result);
-        $this->assertEquals('FREQ=DAILY;BYHOUR=10;BYMINUTE=30;BYSECOND=0;UNTIL=20150616T153000Z', $property->getValue());
+        self::assertEmpty($result);
+        self::assertEquals('FREQ=DAILY;BYHOUR=10;BYMINUTE=30;BYSECOND=0;UNTIL=20150616T153000Z', $property->getValue());
     }
 
-    public function testValidateValidByWeekNoWithRepair()
+    public function testValidateValidByWeekNoWithRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYWEEKNO=11');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(0, $result);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYWEEKNO=11', $property->getValue());
+        self::assertCount(0, $result);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYWEEKNO=11', $property->getValue());
     }
 
-    public function testValidateInvalidByWeekNoWithRepair()
+    public function testValidateInvalidByWeekNoWithRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYWEEKNO=55;BYDAY=WE');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(1, $result);
-        $this->assertEquals('BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!', $result[0]['message']);
-        $this->assertEquals(1, $result[0]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYDAY=WE', $property->getValue());
+        self::assertCount(1, $result);
+        self::assertEquals('BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!', $result[0]['message']);
+        self::assertEquals(1, $result[0]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYDAY=WE', $property->getValue());
     }
 
-    public function testValidateMultipleInvalidByWeekNoWithRepair()
+    public function testValidateMultipleInvalidByWeekNoWithRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYWEEKNO=55,2,-80;BYDAY=WE');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(2, $result);
-        $this->assertEquals('BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!', $result[0]['message']);
-        $this->assertEquals(1, $result[0]['level']);
-        $this->assertEquals('BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!', $result[1]['message']);
-        $this->assertEquals(1, $result[1]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYWEEKNO=2;BYDAY=WE', $property->getValue());
+        self::assertCount(2, $result);
+        self::assertEquals('BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!', $result[0]['message']);
+        self::assertEquals(1, $result[0]['level']);
+        self::assertEquals('BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!', $result[1]['message']);
+        self::assertEquals(1, $result[1]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYWEEKNO=2;BYDAY=WE', $property->getValue());
     }
 
-    public function testValidateAllInvalidByWeekNoWithRepair()
+    public function testValidateAllInvalidByWeekNoWithRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYWEEKNO=55,-80;BYDAY=WE');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(2, $result);
-        $this->assertEquals('BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!', $result[0]['message']);
-        $this->assertEquals(1, $result[0]['level']);
-        $this->assertEquals('BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!', $result[1]['message']);
-        $this->assertEquals(1, $result[1]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYDAY=WE', $property->getValue());
+        self::assertCount(2, $result);
+        self::assertEquals('BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!', $result[0]['message']);
+        self::assertEquals(1, $result[0]['level']);
+        self::assertEquals('BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!', $result[1]['message']);
+        self::assertEquals(1, $result[1]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYDAY=WE', $property->getValue());
     }
 
-    public function testValidateInvalidByWeekNoWithoutRepair()
+    public function testValidateInvalidByWeekNoWithoutRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYWEEKNO=55;BYDAY=WE');
         $result = $property->validate();
 
-        $this->assertCount(1, $result);
-        $this->assertEquals('BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!', $result[0]['message']);
-        $this->assertEquals(3, $result[0]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYWEEKNO=55;BYDAY=WE', $property->getValue());
+        self::assertCount(1, $result);
+        self::assertEquals('BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!', $result[0]['message']);
+        self::assertEquals(3, $result[0]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYWEEKNO=55;BYDAY=WE', $property->getValue());
     }
 
-    public function testValidateValidByYearDayWithRepair()
+    public function testValidateValidByYearDayWithRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYYEARDAY=119');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(0, $result);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYYEARDAY=119', $property->getValue());
+        self::assertCount(0, $result);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYYEARDAY=119', $property->getValue());
     }
 
-    public function testValidateInvalidByYearDayWithRepair()
+    public function testValidateInvalidByYearDayWithRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYYEARDAY=367;BYDAY=WE');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(1, $result);
-        $this->assertEquals('BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!', $result[0]['message']);
-        $this->assertEquals(1, $result[0]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYDAY=WE', $property->getValue());
+        self::assertCount(1, $result);
+        self::assertEquals('BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!', $result[0]['message']);
+        self::assertEquals(1, $result[0]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYDAY=WE', $property->getValue());
     }
 
-    public function testValidateMultipleInvalidByYearDayWithRepair()
+    public function testValidateMultipleInvalidByYearDayWithRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYYEARDAY=380,2,-390;BYDAY=WE');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(2, $result);
-        $this->assertEquals('BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!', $result[0]['message']);
-        $this->assertEquals(1, $result[0]['level']);
-        $this->assertEquals('BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!', $result[1]['message']);
-        $this->assertEquals(1, $result[1]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYYEARDAY=2;BYDAY=WE', $property->getValue());
+        self::assertCount(2, $result);
+        self::assertEquals('BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!', $result[0]['message']);
+        self::assertEquals(1, $result[0]['level']);
+        self::assertEquals('BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!', $result[1]['message']);
+        self::assertEquals(1, $result[1]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYYEARDAY=2;BYDAY=WE', $property->getValue());
     }
 
-    public function testValidateAllInvalidByYearDayWithRepair()
+    public function testValidateAllInvalidByYearDayWithRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYYEARDAY=455,-480;BYDAY=WE');
         $result = $property->validate(Node::REPAIR);
 
-        $this->assertCount(2, $result);
-        $this->assertEquals('BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!', $result[0]['message']);
-        $this->assertEquals(1, $result[0]['level']);
-        $this->assertEquals('BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!', $result[1]['message']);
-        $this->assertEquals(1, $result[1]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYDAY=WE', $property->getValue());
+        self::assertCount(2, $result);
+        self::assertEquals('BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!', $result[0]['message']);
+        self::assertEquals(1, $result[0]['level']);
+        self::assertEquals('BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!', $result[1]['message']);
+        self::assertEquals(1, $result[1]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYDAY=WE', $property->getValue());
     }
 
-    public function testValidateInvalidByYearDayWithoutRepair()
+    public function testValidateInvalidByYearDayWithoutRepair(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('RRULE', 'FREQ=YEARLY;COUNT=6;BYYEARDAY=380;BYDAY=WE');
         $result = $property->validate();
 
-        $this->assertCount(1, $result);
-        $this->assertEquals('BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!', $result[0]['message']);
-        $this->assertEquals(3, $result[0]['level']);
-        $this->assertEquals('FREQ=YEARLY;COUNT=6;BYYEARDAY=380;BYDAY=WE', $property->getValue());
+        self::assertCount(1, $result);
+        self::assertEquals('BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!', $result[0]['message']);
+        self::assertEquals(3, $result[0]['level']);
+        self::assertEquals('FREQ=YEARLY;COUNT=6;BYYEARDAY=380;BYDAY=WE', $property->getValue());
     }
 }
diff --git a/tests/VObject/Property/TextTest.php b/tests/VObject/Property/TextTest.php
index eea21b1ad..0fa320bfe 100644
--- a/tests/VObject/Property/TextTest.php
+++ b/tests/VObject/Property/TextTest.php
@@ -7,7 +7,7 @@
 
 class TextTest extends TestCase
 {
-    public function assertVCard21Serialization($propValue, $expected)
+    public function assertVCard21Serialization($propValue, string $expected): void
     {
         $doc = new VCard([
             'VERSION' => '2.1',
@@ -21,50 +21,50 @@ public function assertVCard21Serialization($propValue, $expected)
 
         $output = $doc->serialize();
 
-        $this->assertEquals("BEGIN:VCARD\r\nVERSION:2.1\r\n$expected\r\nEND:VCARD\r\n", $output);
+        self::assertEquals("BEGIN:VCARD\r\nVERSION:2.1\r\n$expected\r\nEND:VCARD\r\n", $output);
     }
 
-    public function testSerializeVCard21()
+    public function testSerializeVCard21(): void
     {
-        $this->assertVCard21Serialization(
+        self::assertVCard21Serialization(
             'f;oo',
             'PROP;P1=V1:f;oo'
         );
     }
 
-    public function testSerializeVCard21Array()
+    public function testSerializeVCard21Array(): void
     {
-        $this->assertVCard21Serialization(
+        self::assertVCard21Serialization(
             ['f;oo', 'bar'],
             'PROP;P1=V1:f\;oo;bar'
         );
     }
 
-    public function testSerializeVCard21Fold()
+    public function testSerializeVCard21Fold(): void
     {
-        $this->assertVCard21Serialization(
+        self::assertVCard21Serialization(
             str_repeat('x', 80),
             'PROP;P1=V1:'.str_repeat('x', 64)."\r\n ".str_repeat('x', 16)
         );
     }
 
-    public function testSerializeQuotedPrintable()
+    public function testSerializeQuotedPrintable(): void
     {
-        $this->assertVCard21Serialization(
+        self::assertVCard21Serialization(
             "foo\r\nbar",
             'PROP;P1=V1;ENCODING=QUOTED-PRINTABLE:foo=0D=0Abar'
         );
     }
 
-    public function testSerializeQuotedPrintableFold()
+    public function testSerializeQuotedPrintableFold(): void
     {
-        $this->assertVCard21Serialization(
+        self::assertVCard21Serialization(
             "foo\r\nbarxxxxxxxxxxxxxxxxxxxxxxxxxxxxx",
             "PROP;P1=V1;ENCODING=QUOTED-PRINTABLE:foo=0D=0Abarxxxxxxxxxxxxxxxxxxxxxxxxxx=\r\n xxx"
         );
     }
 
-    public function testValidateMinimumPropValue()
+    public function testValidateMinimumPropValue(): void
     {
         $vcard = <<<IN
 BEGIN:VCARD
@@ -76,12 +76,12 @@ public function testValidateMinimumPropValue()
 IN;
 
         $vcard = \Sabre\VObject\Reader::read($vcard);
-        $this->assertEquals(1, count($vcard->validate()));
+        self::assertCount(1, $vcard->validate());
 
-        $this->assertEquals(1, count($vcard->N->getParts()));
+        self::assertCount(1, $vcard->N->getParts());
 
         $vcard->validate(\Sabre\VObject\Node::REPAIR);
 
-        $this->assertEquals(5, count($vcard->N->getParts()));
+        self::assertCount(5, $vcard->N->getParts());
     }
 }
diff --git a/tests/VObject/Property/UriTest.php b/tests/VObject/Property/UriTest.php
index d3d0e0f9c..edb7cc393 100644
--- a/tests/VObject/Property/UriTest.php
+++ b/tests/VObject/Property/UriTest.php
@@ -7,7 +7,7 @@
 
 class UriTest extends TestCase
 {
-    public function testAlwaysEncodeUriVCalendar()
+    public function testAlwaysEncodeUriVCalendar(): void
     {
         // Apple iCal has issues with URL properties that don't have
         // VALUE=URI specified. We added a workaround to vobject that
@@ -21,6 +21,6 @@ public function testAlwaysEncodeUriVCalendar()
 END:VCALENDAR
 ICS;
         $output = Reader::read($input)->serialize();
-        $this->assertStringContainsString('URL;VALUE=URI:http://example.org/', $output);
+        self::assertStringContainsString('URL;VALUE=URI:http://example.org/', $output);
     }
 }
diff --git a/tests/VObject/Property/VCard/DateAndOrTimeTest.php b/tests/VObject/Property/VCard/DateAndOrTimeTest.php
index f21b408a1..8e2cb3207 100644
--- a/tests/VObject/Property/VCard/DateAndOrTimeTest.php
+++ b/tests/VObject/Property/VCard/DateAndOrTimeTest.php
@@ -11,15 +11,15 @@ class DateAndOrTimeTest extends TestCase
     /**
      * @dataProvider dates
      */
-    public function testGetJsonValue($input, $output)
+    public function testGetJsonValue(string $input, string $output): void
     {
         $vcard = new VObject\Component\VCard();
         $prop = $vcard->createProperty('BDAY', $input);
 
-        $this->assertEquals([$output], $prop->getJsonValue());
+        self::assertEquals([$output], $prop->getJsonValue());
     }
 
-    public function dates()
+    public function dates(): array
     {
         return [
             [
@@ -81,7 +81,7 @@ public function dates()
         ];
     }
 
-    public function testSetParts()
+    public function testSetParts(): void
     {
         $vcard = new VObject\Component\VCard();
 
@@ -90,10 +90,10 @@ public function testSetParts()
             new \DateTime('2014-04-02 18:37:00'),
         ]);
 
-        $this->assertEquals('20140402T183700Z', $prop->getValue());
+        self::assertEquals('20140402T183700Z', $prop->getValue());
     }
 
-    public function testSetPartsDateTimeImmutable()
+    public function testSetPartsDateTimeImmutable(): void
     {
         $vcard = new VObject\Component\VCard();
 
@@ -102,10 +102,10 @@ public function testSetPartsDateTimeImmutable()
             new \DateTimeImmutable('2014-04-02 18:37:00'),
         ]);
 
-        $this->assertEquals('20140402T183700Z', $prop->getValue());
+        self::assertEquals('20140402T183700Z', $prop->getValue());
     }
 
-    public function testSetPartsTooMany()
+    public function testSetPartsTooMany(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $vcard = new VObject\Component\VCard();
@@ -117,7 +117,7 @@ public function testSetPartsTooMany()
         ]);
     }
 
-    public function testSetPartsString()
+    public function testSetPartsString(): void
     {
         $vcard = new VObject\Component\VCard();
 
@@ -126,10 +126,10 @@ public function testSetPartsString()
             '20140402T183700Z',
         ]);
 
-        $this->assertEquals('20140402T183700Z', $prop->getValue());
+        self::assertEquals('20140402T183700Z', $prop->getValue());
     }
 
-    public function testSetValueDateTime()
+    public function testSetValueDateTime(): void
     {
         $vcard = new VObject\Component\VCard();
 
@@ -138,10 +138,10 @@ public function testSetValueDateTime()
             new \DateTime('2014-04-02 18:37:00')
         );
 
-        $this->assertEquals('20140402T183700Z', $prop->getValue());
+        self::assertEquals('20140402T183700Z', $prop->getValue());
     }
 
-    public function testSetValueDateTimeImmutable()
+    public function testSetValueDateTimeImmutable(): void
     {
         $vcard = new VObject\Component\VCard();
 
@@ -150,10 +150,10 @@ public function testSetValueDateTimeImmutable()
             new \DateTimeImmutable('2014-04-02 18:37:00')
         );
 
-        $this->assertEquals('20140402T183700Z', $prop->getValue());
+        self::assertEquals('20140402T183700Z', $prop->getValue());
     }
 
-    public function testSetDateTimeOffset()
+    public function testSetDateTimeOffset(): void
     {
         $vcard = new VObject\Component\VCard();
 
@@ -162,10 +162,10 @@ public function testSetDateTimeOffset()
             new \DateTime('2014-04-02 18:37:00', new \DateTimeZone('America/Toronto'))
         );
 
-        $this->assertEquals('20140402T183700-0400', $prop->getValue());
+        self::assertEquals('20140402T183700-0400', $prop->getValue());
     }
 
-    public function testGetDateTime()
+    public function testGetDateTime(): void
     {
         $datetime = new \DateTime('2014-04-02 18:37:00', new \DateTimeZone('America/Toronto'));
 
@@ -173,21 +173,21 @@ public function testGetDateTime()
         $prop = $vcard->createProperty('BDAY', $datetime);
 
         $dt = $prop->getDateTime();
-        $this->assertEquals('2014-04-02T18:37:00-04:00', $dt->format('c'), 'For some reason this one failed. Current default timezone is: '.date_default_timezone_get());
+        self::assertEquals('2014-04-02T18:37:00-04:00', $dt->format('c'), 'For some reason this one failed. Current default timezone is: '.date_default_timezone_get());
     }
 
-    public function testGetDate()
+    public function testGetDate(): void
     {
         $datetime = new \DateTime('2014-04-02');
 
         $vcard = new VObject\Component\VCard();
         $prop = $vcard->createProperty('BDAY', $datetime, null, 'DATE');
 
-        $this->assertEquals('DATE', $prop->getValueType());
-        $this->assertEquals('BDAY:20140402', rtrim($prop->serialize()));
+        self::assertEquals('DATE', $prop->getValueType());
+        self::assertEquals('BDAY:20140402', rtrim($prop->serialize()));
     }
 
-    public function testGetDateIncomplete()
+    public function testGetDateIncomplete(): void
     {
         $datetime = '--0407';
 
@@ -202,10 +202,10 @@ public function testGetDateIncomplete()
         $current = new \DateTime('now');
         $year = $current->format('Y');
 
-        $this->assertEquals($year.'0407', $dt->format('Ymd'));
+        self::assertEquals($year.'0407', $dt->format('Ymd'));
     }
 
-    public function testGetDateIncompleteFromVCard()
+    public function testGetDateIncompleteFromVCard(): void
     {
         $vcard = <<<VCF
 BEGIN:VCARD
@@ -224,27 +224,27 @@ public function testGetDateIncompleteFromVCard()
         $current = new \DateTime('now');
         $year = $current->format('Y');
 
-        $this->assertEquals($year.'0407', $dt->format('Ymd'));
+        self::assertEquals($year.'0407', $dt->format('Ymd'));
     }
 
-    public function testValidate()
+    public function testValidate(): void
     {
         $datetime = '--0407';
 
         $vcard = new VObject\Component\VCard();
         $prop = $vcard->add('BDAY', $datetime);
 
-        $this->assertEquals([], $prop->validate());
+        self::assertEquals([], $prop->validate());
     }
 
-    public function testValidateBroken()
+    public function testValidateBroken(): void
     {
         $datetime = '123';
 
         $vcard = new VObject\Component\VCard();
         $prop = $vcard->add('BDAY', $datetime);
 
-        $this->assertEquals([[
+        self::assertEquals([[
             'level' => 3,
             'message' => 'The supplied value (123) is not a correct DATE-AND-OR-TIME property',
             'node' => $prop,
diff --git a/tests/VObject/Property/VCard/LanguageTagTest.php b/tests/VObject/Property/VCard/LanguageTagTest.php
index 54106ffe8..be3d5c62f 100644
--- a/tests/VObject/Property/VCard/LanguageTagTest.php
+++ b/tests/VObject/Property/VCard/LanguageTagTest.php
@@ -7,39 +7,39 @@
 
 class LanguageTagTest extends TestCase
 {
-    public function testMimeDir()
+    public function testMimeDir(): void
     {
         $input = "BEGIN:VCARD\r\nVERSION:4.0\r\nLANG:nl\r\nEND:VCARD\r\n";
         $mimeDir = new VObject\Parser\MimeDir($input);
 
         $result = $mimeDir->parse($input);
 
-        $this->assertInstanceOf(LanguageTag::class, $result->LANG);
+        self::assertInstanceOf(LanguageTag::class, $result->LANG);
 
-        $this->assertEquals('nl', $result->LANG->getValue());
+        self::assertEquals('nl', $result->LANG->getValue());
 
-        $this->assertEquals(
+        self::assertEquals(
             $input,
             $result->serialize()
         );
     }
 
-    public function testChangeAndSerialize()
+    public function testChangeAndSerialize(): void
     {
         $input = "BEGIN:VCARD\r\nVERSION:4.0\r\nLANG:nl\r\nEND:VCARD\r\n";
         $mimeDir = new VObject\Parser\MimeDir($input);
 
         $result = $mimeDir->parse($input);
 
-        $this->assertInstanceOf(LanguageTag::class, $result->LANG);
+        self::assertInstanceOf(LanguageTag::class, $result->LANG);
         // This replicates what the vcard converter does and triggered a bug in
         // the past.
         $result->LANG->setValue(['de']);
 
-        $this->assertEquals('de', $result->LANG->getValue());
+        self::assertEquals('de', $result->LANG->getValue());
 
         $expected = "BEGIN:VCARD\r\nVERSION:4.0\r\nLANG:de\r\nEND:VCARD\r\n";
-        $this->assertEquals(
+        self::assertEquals(
             $expected,
             $result->serialize()
         );
diff --git a/tests/VObject/Property/VCard/PhoneNumberTest.php b/tests/VObject/Property/VCard/PhoneNumberTest.php
index 668bc7e4c..f9882cdfb 100644
--- a/tests/VObject/Property/VCard/PhoneNumberTest.php
+++ b/tests/VObject/Property/VCard/PhoneNumberTest.php
@@ -7,13 +7,13 @@
 
 class PhoneNumberTest extends TestCase
 {
-    public function testParser()
+    public function testParser(): void
     {
         $input = "BEGIN:VCARD\r\nVERSION:3.0\r\nTEL;TYPE=HOME;VALUE=PHONE-NUMBER:+1234\r\nEND:VCARD\r\n";
 
         $vCard = VObject\Reader::read($input);
-        $this->assertInstanceOf(PhoneNumber::class, $vCard->TEL);
-        $this->assertEquals('PHONE-NUMBER', $vCard->TEL->getValueType());
-        $this->assertEquals($input, $vCard->serialize());
+        self::assertInstanceOf(PhoneNumber::class, $vCard->TEL);
+        self::assertEquals('PHONE-NUMBER', $vCard->TEL->getValueType());
+        self::assertEquals($input, $vCard->serialize());
     }
 }
diff --git a/tests/VObject/PropertyTest.php b/tests/VObject/PropertyTest.php
index 1f6e07022..b15e06b27 100644
--- a/tests/VObject/PropertyTest.php
+++ b/tests/VObject/PropertyTest.php
@@ -8,18 +8,18 @@
 
 class PropertyTest extends TestCase
 {
-    public function testToString()
+    public function testToString(): void
     {
         $cal = new VCalendar();
 
         $property = $cal->createProperty('propname', 'propvalue');
-        $this->assertEquals('PROPNAME', $property->name);
-        $this->assertEquals('propvalue', $property->__toString());
-        $this->assertEquals('propvalue', (string) $property);
-        $this->assertEquals('propvalue', $property->getValue());
+        self::assertEquals('PROPNAME', $property->name);
+        self::assertEquals('propvalue', $property->__toString());
+        self::assertEquals('propvalue', (string) $property);
+        self::assertEquals('propvalue', $property->getValue());
     }
 
-    public function testCreate()
+    public function testCreate(): void
     {
         $cal = new VCalendar();
 
@@ -30,92 +30,92 @@ public function testCreate()
 
         $property = $cal->createProperty('propname', 'propvalue', $params);
 
-        $this->assertEquals('value1', $property['param1']->getValue());
-        $this->assertEquals('value2', $property['param2']->getValue());
+        self::assertEquals('value1', $property['param1']->getValue());
+        self::assertEquals('value2', $property['param2']->getValue());
     }
 
-    public function testSetValue()
+    public function testSetValue(): void
     {
         $cal = new VCalendar();
 
         $property = $cal->createProperty('propname', 'propvalue');
         $property->setValue('value2');
 
-        $this->assertEquals('PROPNAME', $property->name);
-        $this->assertEquals('value2', $property->__toString());
+        self::assertEquals('PROPNAME', $property->name);
+        self::assertEquals('value2', $property->__toString());
     }
 
-    public function testParameterExists()
+    public function testParameterExists(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('propname', 'propvalue');
         $property['paramname'] = 'paramvalue';
 
-        $this->assertTrue(isset($property['PARAMNAME']));
-        $this->assertTrue(isset($property['paramname']));
-        $this->assertFalse(isset($property['foo']));
+        self::assertTrue(isset($property['PARAMNAME']));
+        self::assertTrue(isset($property['paramname']));
+        self::assertFalse(isset($property['foo']));
     }
 
-    public function testParameterGet()
+    public function testParameterGet(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('propname', 'propvalue');
         $property['paramname'] = 'paramvalue';
 
-        $this->assertInstanceOf(Parameter::class, $property['paramname']);
+        self::assertInstanceOf(Parameter::class, $property['paramname']);
     }
 
-    public function testParameterNotExists()
+    public function testParameterNotExists(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('propname', 'propvalue');
         $property['paramname'] = 'paramvalue';
 
-        $this->assertNull($property['foo']);
+        self::assertNull($property['foo']);
     }
 
-    public function testParameterMultiple()
+    public function testParameterMultiple(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('propname', 'propvalue');
         $property['paramname'] = 'paramvalue';
         $property->add('paramname', 'paramvalue');
 
-        $this->assertInstanceOf(Parameter::class, $property['paramname']);
-        $this->assertEquals(2, count($property['paramname']->getParts()));
+        self::assertInstanceOf(Parameter::class, $property['paramname']);
+        self::assertCount(2, $property['paramname']->getParts());
     }
 
-    public function testSetParameterAsString()
+    public function testSetParameterAsString(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('propname', 'propvalue');
         $property['paramname'] = 'paramvalue';
 
-        $this->assertEquals(1, count($property->parameters()));
-        $this->assertInstanceOf(Parameter::class, $property->parameters['PARAMNAME']);
-        $this->assertEquals('PARAMNAME', $property->parameters['PARAMNAME']->name);
-        $this->assertEquals('paramvalue', $property->parameters['PARAMNAME']->getValue());
+        self::assertCount(1, $property->parameters());
+        self::assertInstanceOf(Parameter::class, $property->parameters['PARAMNAME']);
+        self::assertEquals('PARAMNAME', $property->parameters['PARAMNAME']->name);
+        self::assertEquals('paramvalue', $property->parameters['PARAMNAME']->getValue());
     }
 
-    public function testUnsetParameter()
+    public function testUnsetParameter(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('propname', 'propvalue');
         $property['paramname'] = 'paramvalue';
 
         unset($property['PARAMNAME']);
-        $this->assertEquals(0, count($property->parameters()));
+        self::assertCount(0, $property->parameters());
     }
 
-    public function testSerialize()
+    public function testSerialize(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('propname', 'propvalue');
 
-        $this->assertEquals("PROPNAME:propvalue\r\n", $property->serialize());
+        self::assertEquals("PROPNAME:propvalue\r\n", $property->serialize());
     }
 
-    public function testSerializeParam()
+    public function testSerializeParam(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('propname', 'propvalue', [
@@ -123,18 +123,18 @@ public function testSerializeParam()
             'paramname2' => 'paramvalue2',
         ]);
 
-        $this->assertEquals("PROPNAME;PARAMNAME=paramvalue;PARAMNAME2=paramvalue2:propvalue\r\n", $property->serialize());
+        self::assertEquals("PROPNAME;PARAMNAME=paramvalue;PARAMNAME2=paramvalue2:propvalue\r\n", $property->serialize());
     }
 
-    public function testSerializeNewLine()
+    public function testSerializeNewLine(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('SUMMARY', "line1\nline2");
 
-        $this->assertEquals("SUMMARY:line1\\nline2\r\n", $property->serialize());
+        self::assertEquals("SUMMARY:line1\\nline2\r\n", $property->serialize());
     }
 
-    public function testSerializeLongLine()
+    public function testSerializeLongLine(): void
     {
         $cal = new VCalendar();
         $value = str_repeat('!', 200);
@@ -142,10 +142,10 @@ public function testSerializeLongLine()
 
         $expected = 'PROPNAME:'.str_repeat('!', 66)."\r\n ".str_repeat('!', 74)."\r\n ".str_repeat('!', 60)."\r\n";
 
-        $this->assertEquals($expected, $property->serialize());
+        self::assertEquals($expected, $property->serialize());
     }
 
-    public function testSerializeUTF8LineFold()
+    public function testSerializeUTF8LineFold(): void
     {
         $cal = new VCalendar();
         $value = str_repeat('!', 65)."\xc3\xa4bla".str_repeat('!', 142)."\xc3\xa4foo"; // inserted umlaut-a
@@ -156,53 +156,53 @@ public function testSerializeUTF8LineFold()
         //  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! (" "         + 73x"!" = 74 bytes)
         //  äfoo
         $expected = 'PROPNAME:'.str_repeat('!', 65)."\r\n \xc3\xa4bla".str_repeat('!', 69)."\r\n ".str_repeat('!', 73)."\r\n \xc3\xa4foo\r\n";
-        $this->assertEquals($expected, $property->serialize());
+        self::assertEquals($expected, $property->serialize());
     }
 
-    public function testGetIterator()
+    public function testGetIterator(): void
     {
         $cal = new VCalendar();
         $it = new ElementList([]);
         $property = $cal->createProperty('propname', 'propvalue');
         $property->setIterator($it);
-        $this->assertEquals($it, $property->getIterator());
+        self::assertEquals($it, $property->getIterator());
     }
 
-    public function testGetIteratorDefault()
+    public function testGetIteratorDefault(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('propname', 'propvalue');
         $it = $property->getIterator();
-        $this->assertTrue($it instanceof ElementList);
-        $this->assertEquals(1, count($it));
+        self::assertTrue($it instanceof ElementList);
+        self::assertCount(1, $it);
     }
 
-    public function testAddScalar()
+    public function testAddScalar(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('EMAIL');
 
         $property->add('myparam', 'value');
 
-        $this->assertEquals(1, count($property->parameters()));
+        self::assertCount(1, $property->parameters());
 
-        $this->assertTrue($property->parameters['MYPARAM'] instanceof Parameter);
-        $this->assertEquals('MYPARAM', $property->parameters['MYPARAM']->name);
-        $this->assertEquals('value', $property->parameters['MYPARAM']->getValue());
+        self::assertTrue($property->parameters['MYPARAM'] instanceof Parameter);
+        self::assertEquals('MYPARAM', $property->parameters['MYPARAM']->name);
+        self::assertEquals('value', $property->parameters['MYPARAM']->getValue());
     }
 
-    public function testAddParameter()
+    public function testAddParameter(): void
     {
         $cal = new VCalendar();
         $prop = $cal->createProperty('EMAIL');
 
         $prop->add('MYPARAM', 'value');
 
-        $this->assertEquals(1, count($prop->parameters()));
-        $this->assertEquals('MYPARAM', $prop['myparam']->name);
+        self::assertCount(1, $prop->parameters());
+        self::assertEquals('MYPARAM', $prop['myparam']->name);
     }
 
-    public function testAddParameterTwice()
+    public function testAddParameterTwice(): void
     {
         $cal = new VCalendar();
         $prop = $cal->createProperty('EMAIL');
@@ -210,13 +210,13 @@ public function testAddParameterTwice()
         $prop->add('MYPARAM', 'value1');
         $prop->add('MYPARAM', 'value2');
 
-        $this->assertEquals(1, count($prop->parameters));
-        $this->assertEquals(2, count($prop->parameters['MYPARAM']->getParts()));
+        self::assertCount(1, $prop->parameters);
+        self::assertCount(2, $prop->parameters['MYPARAM']->getParts());
 
-        $this->assertEquals('MYPARAM', $prop['MYPARAM']->name);
+        self::assertEquals('MYPARAM', $prop['MYPARAM']->name);
     }
 
-    public function testClone()
+    public function testClone(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('EMAIL', 'value');
@@ -225,10 +225,10 @@ public function testClone()
         $property2 = clone $property;
 
         $property['FOO'] = 'BAZ';
-        $this->assertEquals('BAR', (string) $property2['FOO']);
+        self::assertEquals('BAR', (string) $property2['FOO']);
     }
 
-    public function testCreateParams()
+    public function testCreateParams(): void
     {
         $cal = new VCalendar();
         $property = $cal->createProperty('X-PROP', 'value', [
@@ -236,21 +236,21 @@ public function testCreateParams()
             'param2' => ['value2', 'value3'],
         ]);
 
-        $this->assertEquals(1, count($property['PARAM1']->getParts()));
-        $this->assertEquals(2, count($property['PARAM2']->getParts()));
+        self::assertCount(1, $property['PARAM1']->getParts());
+        self::assertCount(2, $property['PARAM2']->getParts());
     }
 
-    public function testValidateNonUTF8()
+    public function testValidateNonUTF8(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('X-PROP', "Bla\x00");
         $result = $property->validate(Property::REPAIR);
 
-        $this->assertEquals('Property contained a control character (0x00)', $result[0]['message']);
-        $this->assertEquals('Bla', $property->getValue());
+        self::assertEquals('Property contained a control character (0x00)', $result[0]['message']);
+        self::assertEquals('Bla', $property->getValue());
     }
 
-    public function testValidateControlChars()
+    public function testValidateControlChars(): void
     {
         $s = 'chars[';
         foreach ([
@@ -268,48 +268,54 @@ public function testValidateControlChars()
         $property = $calendar->createProperty('X-PROP', $s);
         $result = $property->validate(Property::REPAIR);
 
-        $this->assertEquals('Property contained a control character (0x7f)', $result[0]['message']);
-        $this->assertEquals("chars[7F()5E(^)5C(\\\\)3B(\\;)3A(:)2C(\\,)22(\")20( )1F()1E()1D()1C()1B()1A()19()18()17()16()15()14()13()12()11()10()0F()0E()0D()0C()0B()0A(\\n)09(\t)08()07()06()05()04()03()02()01()00()]end", $property->getRawMimeDirValue());
+        self::assertEquals('Property contained a control character (0x7f)', $result[0]['message']);
+        self::assertEquals("chars[7F()5E(^)5C(\\\\)3B(\\;)3A(:)2C(\\,)22(\")20( )1F()1E()1D()1C()1B()1A()19()18()17()16()15()14()13()12()11()10()0F()0E()0D()0C()0B()0A(\\n)09(\t)08()07()06()05()04()03()02()01()00()]end", $property->getRawMimeDirValue());
     }
 
-    public function testValidateBadPropertyName()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testValidateBadPropertyName(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('X_*&PROP*', 'Bla');
-        $result = $property->validate(Property::REPAIR);
+        $result = $property->validate(Node::REPAIR);
 
-        $this->assertEquals($result[0]['message'], 'The propertyname: X_*&PROP* contains invalid characters. Only A-Z, 0-9 and - are allowed');
-        $this->assertEquals('X-PROP', $property->name);
+        self::assertEquals('The property name: X_*&PROP* contains invalid characters. Only A-Z, 0-9 and - are allowed', $result[0]['message']);
+        self::assertEquals('X-PROP', $property->name);
     }
 
-    public function testGetValue()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testGetValue(): void
     {
         $calendar = new VCalendar();
         $property = $calendar->createProperty('SUMMARY', null);
-        $this->assertEquals([], $property->getParts());
-        $this->assertNull($property->getValue());
+        self::assertEquals([], $property->getParts());
+        self::assertNull($property->getValue());
 
         $property->setValue([]);
-        $this->assertEquals([], $property->getParts());
-        $this->assertNull($property->getValue());
+        self::assertEquals([], $property->getParts());
+        self::assertNull($property->getValue());
 
         $property->setValue([1]);
-        $this->assertEquals([1], $property->getParts());
-        $this->assertEquals(1, $property->getValue());
+        self::assertEquals([1], $property->getParts());
+        self::assertEquals(1, $property->getValue());
 
         $property->setValue([1, 2]);
-        $this->assertEquals([1, 2], $property->getParts());
-        $this->assertEquals('1,2', $property->getValue());
+        self::assertEquals([1, 2], $property->getParts());
+        self::assertEquals('1,2', $property->getValue());
 
         $property->setValue('str');
-        $this->assertEquals(['str'], $property->getParts());
-        $this->assertEquals('str', $property->getValue());
+        self::assertEquals(['str'], $property->getParts());
+        self::assertEquals('str', $property->getValue());
     }
 
     /**
      * ElementList should reject this.
      */
-    public function testArrayAccessSetInt()
+    public function testArrayAccessSetInt(): void
     {
         $this->expectException(\LogicException::class);
         $calendar = new VCalendar();
@@ -322,7 +328,7 @@ public function testArrayAccessSetInt()
     /**
      * ElementList should reject this.
      */
-    public function testArrayAccessUnsetInt()
+    public function testArrayAccessUnsetInt(): void
     {
         $this->expectException(\LogicException::class);
         $calendar = new VCalendar();
@@ -332,7 +338,7 @@ public function testArrayAccessUnsetInt()
         unset($calendar->{'X-PROP'}[0]);
     }
 
-    public function testValidateBadEncoding()
+    public function testValidateBadEncoding(): void
     {
         $document = new VCalendar();
         $property = $document->add('X-FOO', 'value');
@@ -340,11 +346,11 @@ public function testValidateBadEncoding()
 
         $result = $property->validate();
 
-        $this->assertEquals('ENCODING=INVALID is not valid for this document type.', $result[0]['message']);
-        $this->assertEquals(3, $result[0]['level']);
+        self::assertEquals('ENCODING=INVALID is not valid for this document type.', $result[0]['message']);
+        self::assertEquals(3, $result[0]['level']);
     }
 
-    public function testValidateBadEncodingVCard4()
+    public function testValidateBadEncodingVCard4(): void
     {
         $document = new VCard(['VERSION' => '4.0']);
         $property = $document->add('X-FOO', 'value');
@@ -352,11 +358,11 @@ public function testValidateBadEncodingVCard4()
 
         $result = $property->validate();
 
-        $this->assertEquals('ENCODING parameter is not valid in vCard 4.', $result[0]['message']);
-        $this->assertEquals(3, $result[0]['level']);
+        self::assertEquals('ENCODING parameter is not valid in vCard 4.', $result[0]['message']);
+        self::assertEquals(3, $result[0]['level']);
     }
 
-    public function testValidateBadEncodingVCard3()
+    public function testValidateBadEncodingVCard3(): void
     {
         $document = new VCard(['VERSION' => '3.0']);
         $property = $document->add('X-FOO', 'value');
@@ -364,17 +370,17 @@ public function testValidateBadEncodingVCard3()
 
         $result = $property->validate();
 
-        $this->assertEquals('ENCODING=BASE64 is not valid for this document type.', $result[0]['message']);
-        $this->assertEquals(3, $result[0]['level']);
+        self::assertEquals('ENCODING=BASE64 is not valid for this document type.', $result[0]['message']);
+        self::assertEquals(3, $result[0]['level']);
 
-        //Validate the reparation of BASE64 formatted vCard v3
+        // Validate the reparation of BASE64 formatted vCard v3
         $result = $property->validate(Property::REPAIR);
 
-        $this->assertEquals('ENCODING=BASE64 has been transformed to ENCODING=B.', $result[0]['message']);
-        $this->assertEquals(1, $result[0]['level']);
+        self::assertEquals('ENCODING=BASE64 has been transformed to ENCODING=B.', $result[0]['message']);
+        self::assertEquals(1, $result[0]['level']);
     }
 
-    public function testValidateBadEncodingVCard21()
+    public function testValidateBadEncodingVCard21(): void
     {
         $document = new VCard(['VERSION' => '2.1']);
         $property = $document->add('X-FOO', 'value');
@@ -382,7 +388,7 @@ public function testValidateBadEncodingVCard21()
 
         $result = $property->validate();
 
-        $this->assertEquals('ENCODING=B is not valid for this document type.', $result[0]['message']);
-        $this->assertEquals(3, $result[0]['level']);
+        self::assertEquals('ENCODING=B is not valid for this document type.', $result[0]['message']);
+        self::assertEquals(3, $result[0]['level']);
     }
 }
diff --git a/tests/VObject/ReaderTest.php b/tests/VObject/ReaderTest.php
index 96ed56be0..336a291ab 100644
--- a/tests/VObject/ReaderTest.php
+++ b/tests/VObject/ReaderTest.php
@@ -6,18 +6,18 @@
 
 class ReaderTest extends TestCase
 {
-    public function testReadComponent()
+    public function testReadComponent(): void
     {
         $data = "BEGIN:VCALENDAR\r\nEND:VCALENDAR";
 
         $result = Reader::read($data);
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCALENDAR', $result->name);
-        $this->assertEquals(0, count($result->children()));
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCALENDAR', $result->name);
+        self::assertCount(0, $result->children());
     }
 
-    public function testReadStream()
+    public function testReadStream(): void
     {
         $data = "BEGIN:VCALENDAR\r\nEND:VCALENDAR";
 
@@ -27,101 +27,106 @@ public function testReadStream()
 
         $result = Reader::read($stream);
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCALENDAR', $result->name);
-        $this->assertEquals(0, count($result->children()));
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCALENDAR', $result->name);
+        self::assertCount(0, $result->children());
     }
 
-    public function testReadComponentUnixNewLine()
+    public function testReadComponentUnixNewLine(): void
     {
         $data = "BEGIN:VCALENDAR\nEND:VCALENDAR";
 
         $result = Reader::read($data);
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCALENDAR', $result->name);
-        $this->assertEquals(0, count($result->children()));
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCALENDAR', $result->name);
+        self::assertCount(0, $result->children());
     }
 
-    public function testReadComponentLineFold()
+    public function testReadComponentLineFold(): void
     {
         $data = "BEGIN:\r\n\tVCALENDAR\r\nE\r\n ND:VCALENDAR";
 
         $result = Reader::read($data);
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCALENDAR', $result->name);
-        $this->assertEquals(0, count($result->children()));
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCALENDAR', $result->name);
+        self::assertCount(0, $result->children());
     }
 
-    public function testReadCorruptComponent()
+    public function testReadCorruptComponent(): void
     {
         $this->expectException(ParseException::class);
         $data = "BEGIN:VCALENDAR\r\nEND:FOO";
 
-        $result = Reader::read($data);
+        Reader::read($data);
     }
 
-    public function testReadCorruptSubComponent()
+    public function testReadCorruptSubComponent(): void
     {
         $this->expectException(ParseException::class);
         $data = "BEGIN:VCALENDAR\r\nBEGIN:VEVENT\r\nEND:FOO\r\nEND:VCALENDAR";
 
-        $result = Reader::read($data);
+        Reader::read($data);
     }
 
-    public function testReadProperty()
+    public function testReadProperty(): void
     {
         $data = "BEGIN:VCALENDAR\r\nSUMMARY:propValue\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
         $result = $result->SUMMARY;
-        $this->assertInstanceOf(Property::class, $result);
-        $this->assertEquals('SUMMARY', $result->name);
-        $this->assertEquals('propValue', $result->getValue());
+        self::assertInstanceOf(Property::class, $result);
+        self::assertEquals('SUMMARY', $result->name);
+        self::assertEquals('propValue', $result->getValue());
     }
 
-    public function testReadPropertyWithNewLine()
+    public function testReadPropertyWithNewLine(): void
     {
         $data = "BEGIN:VCALENDAR\r\nSUMMARY:Line1\\nLine2\\NLine3\\\\Not the 4th line!\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
         $result = $result->SUMMARY;
-        $this->assertInstanceOf(Property::class, $result);
-        $this->assertEquals('SUMMARY', $result->name);
-        $this->assertEquals("Line1\nLine2\nLine3\\Not the 4th line!", $result->getValue());
+        self::assertInstanceOf(Property::class, $result);
+        self::assertEquals('SUMMARY', $result->name);
+        self::assertEquals("Line1\nLine2\nLine3\\Not the 4th line!", $result->getValue());
     }
 
-    public function testReadMappedProperty()
+    public function testReadMappedProperty(): void
     {
         $data = "BEGIN:VCALENDAR\r\nDTSTART:20110529\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
         $result = $result->DTSTART;
-        $this->assertInstanceOf(Property\ICalendar\DateTime::class, $result);
-        $this->assertEquals('DTSTART', $result->name);
-        $this->assertEquals('20110529', $result->getValue());
+        self::assertInstanceOf(Property\ICalendar\DateTime::class, $result);
+        self::assertEquals('DTSTART', $result->name);
+        self::assertEquals('20110529', $result->getValue());
     }
 
-    public function testReadMappedPropertyGrouped()
+    public function testReadMappedPropertyGrouped(): void
     {
         $data = "BEGIN:VCALENDAR\r\nfoo.DTSTART:20110529\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
         $result = $result->DTSTART;
-        $this->assertInstanceOf(Property\ICalendar\DateTime::class, $result);
-        $this->assertEquals('DTSTART', $result->name);
-        $this->assertEquals('20110529', $result->getValue());
+        self::assertInstanceOf(Property\ICalendar\DateTime::class, $result);
+        self::assertEquals('DTSTART', $result->name);
+        self::assertEquals('20110529', $result->getValue());
     }
 
-    public function testReadBrokenLine()
+    public function testReadMissingEnd(): void
     {
-        $this->expectException(ParseException::class);
-        $data = "BEGIN:VCALENDAR\r\nPROPNAME;propValue";
+        $data = "BEGIN:VCALENDAR\r\nPROPNAME:propValue";
         $result = Reader::read($data);
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCALENDAR', $result->name);
+        self::assertCount(1, $result->children());
+        self::assertInstanceOf(Property::class, $result->children()[0]);
+        self::assertEquals('PROPNAME', $result->children()[0]->name);
+        self::assertEquals('propValue', $result->children()[0]->getValue());
     }
 
-    public function testReadPropertyInComponent()
+    public function testReadPropertyInComponent(): void
     {
         $data = [
             'BEGIN:VCALENDAR',
@@ -131,15 +136,15 @@ public function testReadPropertyInComponent()
 
         $result = Reader::read(implode("\r\n", $data));
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCALENDAR', $result->name);
-        $this->assertEquals(1, count($result->children()));
-        $this->assertInstanceOf(Property::class, $result->children()[0]);
-        $this->assertEquals('PROPNAME', $result->children()[0]->name);
-        $this->assertEquals('propValue', $result->children()[0]->getValue());
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCALENDAR', $result->name);
+        self::assertCount(1, $result->children());
+        self::assertInstanceOf(Property::class, $result->children()[0]);
+        self::assertEquals('PROPNAME', $result->children()[0]->name);
+        self::assertEquals('propValue', $result->children()[0]->getValue());
     }
 
-    public function testReadNestedComponent()
+    public function testReadNestedComponent(): void
     {
         $data = [
             'BEGIN:VCALENDAR',
@@ -152,157 +157,157 @@ public function testReadNestedComponent()
 
         $result = Reader::read(implode("\r\n", $data));
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCALENDAR', $result->name);
-        $this->assertEquals(1, count($result->children()));
-        $this->assertInstanceOf(Component::class, $result->children()[0]);
-        $this->assertEquals('VTIMEZONE', $result->children()[0]->name);
-        $this->assertEquals(1, count($result->children()[0]->children()));
-        $this->assertInstanceOf(Component::class, $result->children()[0]->children()[0]);
-        $this->assertEquals('DAYLIGHT', $result->children()[0]->children()[0]->name);
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCALENDAR', $result->name);
+        self::assertCount(1, $result->children());
+        self::assertInstanceOf(Component::class, $result->children()[0]);
+        self::assertEquals('VTIMEZONE', $result->children()[0]->name);
+        self::assertCount(1, $result->children()[0]->children());
+        self::assertInstanceOf(Component::class, $result->children()[0]->children()[0]);
+        self::assertEquals('DAYLIGHT', $result->children()[0]->children()[0]->name);
     }
 
-    public function testReadPropertyParameter()
+    public function testReadPropertyParameter(): void
     {
         $data = "BEGIN:VCALENDAR\r\nPROPNAME;PARAMNAME=paramvalue:propValue\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
         $result = $result->PROPNAME;
 
-        $this->assertInstanceOf(Property::class, $result);
-        $this->assertEquals('PROPNAME', $result->name);
-        $this->assertEquals('propValue', $result->getValue());
-        $this->assertEquals(1, count($result->parameters()));
-        $this->assertEquals('PARAMNAME', $result->parameters['PARAMNAME']->name);
-        $this->assertEquals('paramvalue', $result->parameters['PARAMNAME']->getValue());
+        self::assertInstanceOf(Property::class, $result);
+        self::assertEquals('PROPNAME', $result->name);
+        self::assertEquals('propValue', $result->getValue());
+        self::assertCount(1, $result->parameters());
+        self::assertEquals('PARAMNAME', $result->parameters['PARAMNAME']->name);
+        self::assertEquals('paramvalue', $result->parameters['PARAMNAME']->getValue());
     }
 
-    public function testReadPropertyRepeatingParameter()
+    public function testReadPropertyRepeatingParameter(): void
     {
         $data = "BEGIN:VCALENDAR\r\nPROPNAME;N=1;N=2;N=3,4;N=\"5\",6;N=\"7,8\";N=9,10;N=^'11^':propValue\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
         $result = $result->PROPNAME;
 
-        $this->assertInstanceOf(Property::class, $result);
-        $this->assertEquals('PROPNAME', $result->name);
-        $this->assertEquals('propValue', $result->getValue());
-        $this->assertEquals(1, count($result->parameters()));
-        $this->assertEquals('N', $result->parameters['N']->name);
-        $this->assertEquals('1,2,3,4,5,6,7,8,9,10,"11"', $result->parameters['N']->getValue());
-        $this->assertEquals([1, 2, 3, 4, 5, 6, '7,8', 9, 10, '"11"'], $result->parameters['N']->getParts());
+        self::assertInstanceOf(Property::class, $result);
+        self::assertEquals('PROPNAME', $result->name);
+        self::assertEquals('propValue', $result->getValue());
+        self::assertCount(1, $result->parameters());
+        self::assertEquals('N', $result->parameters['N']->name);
+        self::assertEquals('1,2,3,4,5,6,7,8,9,10,"11"', $result->parameters['N']->getValue());
+        self::assertEquals([1, 2, 3, 4, 5, 6, '7,8', 9, 10, '"11"'], $result->parameters['N']->getParts());
     }
 
-    public function testReadPropertyRepeatingNamelessGuessedParameter()
+    public function testReadPropertyRepeatingNamelessGuessedParameter(): void
     {
         $data = "BEGIN:VCALENDAR\r\nPROPNAME;WORK;VOICE;PREF:propValue\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
         $result = $result->PROPNAME;
 
-        $this->assertInstanceOf(Property::class, $result);
-        $this->assertEquals('PROPNAME', $result->name);
-        $this->assertEquals('propValue', $result->getValue());
-        $this->assertEquals(1, count($result->parameters()));
-        $this->assertEquals('TYPE', $result->parameters['TYPE']->name);
-        $this->assertEquals('WORK,VOICE,PREF', $result->parameters['TYPE']->getValue());
-        $this->assertEquals(['WORK', 'VOICE', 'PREF'], $result->parameters['TYPE']->getParts());
+        self::assertInstanceOf(Property::class, $result);
+        self::assertEquals('PROPNAME', $result->name);
+        self::assertEquals('propValue', $result->getValue());
+        self::assertCount(1, $result->parameters());
+        self::assertEquals('TYPE', $result->parameters['TYPE']->name);
+        self::assertEquals('WORK,VOICE,PREF', $result->parameters['TYPE']->getValue());
+        self::assertEquals(['WORK', 'VOICE', 'PREF'], $result->parameters['TYPE']->getParts());
     }
 
-    public function testReadPropertyNoName()
+    public function testReadPropertyNoName(): void
     {
         $data = "BEGIN:VCALENDAR\r\nPROPNAME;PRODIGY:propValue\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
         $result = $result->PROPNAME;
 
-        $this->assertInstanceOf(Property::class, $result);
-        $this->assertEquals('PROPNAME', $result->name);
-        $this->assertEquals('propValue', $result->getValue());
-        $this->assertEquals(1, count($result->parameters()));
-        $this->assertEquals('TYPE', $result->parameters['TYPE']->name);
-        $this->assertTrue($result->parameters['TYPE']->noName);
-        $this->assertEquals('PRODIGY', $result->parameters['TYPE']);
+        self::assertInstanceOf(Property::class, $result);
+        self::assertEquals('PROPNAME', $result->name);
+        self::assertEquals('propValue', $result->getValue());
+        self::assertCount(1, $result->parameters());
+        self::assertEquals('TYPE', $result->parameters['TYPE']->name);
+        self::assertTrue($result->parameters['TYPE']->noName);
+        self::assertEquals('PRODIGY', $result->parameters['TYPE']);
     }
 
-    public function testReadPropertyParameterExtraColon()
+    public function testReadPropertyParameterExtraColon(): void
     {
         $data = "BEGIN:VCALENDAR\r\nPROPNAME;PARAMNAME=paramvalue:propValue:anotherrandomstring\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
         $result = $result->PROPNAME;
 
-        $this->assertInstanceOf(Property::class, $result);
-        $this->assertEquals('PROPNAME', $result->name);
-        $this->assertEquals('propValue:anotherrandomstring', $result->getValue());
-        $this->assertEquals(1, count($result->parameters()));
-        $this->assertEquals('PARAMNAME', $result->parameters['PARAMNAME']->name);
-        $this->assertEquals('paramvalue', $result->parameters['PARAMNAME']->getValue());
+        self::assertInstanceOf(Property::class, $result);
+        self::assertEquals('PROPNAME', $result->name);
+        self::assertEquals('propValue:anotherrandomstring', $result->getValue());
+        self::assertCount(1, $result->parameters());
+        self::assertEquals('PARAMNAME', $result->parameters['PARAMNAME']->name);
+        self::assertEquals('paramvalue', $result->parameters['PARAMNAME']->getValue());
     }
 
-    public function testReadProperty2Parameters()
+    public function testReadProperty2Parameters(): void
     {
         $data = "BEGIN:VCALENDAR\r\nPROPNAME;PARAMNAME=paramvalue;PARAMNAME2=paramvalue2:propValue\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
         $result = $result->PROPNAME;
 
-        $this->assertInstanceOf(Property::class, $result);
-        $this->assertEquals('PROPNAME', $result->name);
-        $this->assertEquals('propValue', $result->getValue());
-        $this->assertEquals(2, count($result->parameters()));
-        $this->assertEquals('PARAMNAME', $result->parameters['PARAMNAME']->name);
-        $this->assertEquals('paramvalue', $result->parameters['PARAMNAME']->getValue());
-        $this->assertEquals('PARAMNAME2', $result->parameters['PARAMNAME2']->name);
-        $this->assertEquals('paramvalue2', $result->parameters['PARAMNAME2']->getValue());
+        self::assertInstanceOf(Property::class, $result);
+        self::assertEquals('PROPNAME', $result->name);
+        self::assertEquals('propValue', $result->getValue());
+        self::assertCount(2, $result->parameters());
+        self::assertEquals('PARAMNAME', $result->parameters['PARAMNAME']->name);
+        self::assertEquals('paramvalue', $result->parameters['PARAMNAME']->getValue());
+        self::assertEquals('PARAMNAME2', $result->parameters['PARAMNAME2']->name);
+        self::assertEquals('paramvalue2', $result->parameters['PARAMNAME2']->getValue());
     }
 
-    public function testReadPropertyParameterQuoted()
+    public function testReadPropertyParameterQuoted(): void
     {
         $data = "BEGIN:VCALENDAR\r\nPROPNAME;PARAMNAME=\"paramvalue\":propValue\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
         $result = $result->PROPNAME;
 
-        $this->assertInstanceOf(Property::class, $result);
-        $this->assertEquals('PROPNAME', $result->name);
-        $this->assertEquals('propValue', $result->getValue());
-        $this->assertEquals(1, count($result->parameters()));
-        $this->assertEquals('PARAMNAME', $result->parameters['PARAMNAME']->name);
-        $this->assertEquals('paramvalue', $result->parameters['PARAMNAME']->getValue());
+        self::assertInstanceOf(Property::class, $result);
+        self::assertEquals('PROPNAME', $result->name);
+        self::assertEquals('propValue', $result->getValue());
+        self::assertCount(1, $result->parameters());
+        self::assertEquals('PARAMNAME', $result->parameters['PARAMNAME']->name);
+        self::assertEquals('paramvalue', $result->parameters['PARAMNAME']->getValue());
     }
 
-    public function testReadPropertyParameterNewLines()
+    public function testReadPropertyParameterNewLines(): void
     {
         $data = "BEGIN:VCALENDAR\r\nPROPNAME;PARAMNAME=paramvalue1^nvalue2^^nvalue3:propValue\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
         $result = $result->PROPNAME;
 
-        $this->assertInstanceOf(Property::class, $result);
-        $this->assertEquals('PROPNAME', $result->name);
-        $this->assertEquals('propValue', $result->getValue());
+        self::assertInstanceOf(Property::class, $result);
+        self::assertEquals('PROPNAME', $result->name);
+        self::assertEquals('propValue', $result->getValue());
 
-        $this->assertEquals(1, count($result->parameters()));
-        $this->assertEquals('PARAMNAME', $result->parameters['PARAMNAME']->name);
-        $this->assertEquals("paramvalue1\nvalue2^nvalue3", $result->parameters['PARAMNAME']->getValue());
+        self::assertCount(1, $result->parameters());
+        self::assertEquals('PARAMNAME', $result->parameters['PARAMNAME']->name);
+        self::assertEquals("paramvalue1\nvalue2^nvalue3", $result->parameters['PARAMNAME']->getValue());
     }
 
-    public function testReadPropertyParameterQuotedColon()
+    public function testReadPropertyParameterQuotedColon(): void
     {
         $data = "BEGIN:VCALENDAR\r\nPROPNAME;PARAMNAME=\"param:value\":propValue\r\nEND:VCALENDAR";
         $result = Reader::read($data);
         $result = $result->PROPNAME;
 
-        $this->assertInstanceOf(Property::class, $result);
-        $this->assertEquals('PROPNAME', $result->name);
-        $this->assertEquals('propValue', $result->getValue());
-        $this->assertEquals(1, count($result->parameters()));
-        $this->assertEquals('PARAMNAME', $result->parameters['PARAMNAME']->name);
-        $this->assertEquals('param:value', $result->parameters['PARAMNAME']->getValue());
+        self::assertInstanceOf(Property::class, $result);
+        self::assertEquals('PROPNAME', $result->name);
+        self::assertEquals('propValue', $result->getValue());
+        self::assertCount(1, $result->parameters());
+        self::assertEquals('PARAMNAME', $result->parameters['PARAMNAME']->name);
+        self::assertEquals('param:value', $result->parameters['PARAMNAME']->getValue());
     }
 
-    public function testReadForgiving()
+    public function testReadForgiving(): void
     {
         $data = [
             'BEGIN:VCALENDAR',
@@ -312,12 +317,12 @@ public function testReadForgiving()
 
         $caught = false;
         try {
-            $result = Reader::read(implode("\r\n", $data));
+            Reader::read(implode("\r\n", $data));
         } catch (ParseException $e) {
             $caught = true;
         }
 
-        $this->assertEquals(true, $caught);
+        self::assertEquals(true, $caught);
 
         $result = Reader::read(implode("\r\n", $data), Reader::OPTION_FORGIVING);
 
@@ -328,10 +333,10 @@ public function testReadForgiving()
             '',
         ]);
 
-        $this->assertEquals($expected, $result->serialize());
+        self::assertEquals($expected, $result->serialize());
     }
 
-    public function testReadWithInvalidLine()
+    public function testReadWithInvalidLine(): void
     {
         $data = [
             'BEGIN:VCALENDAR',
@@ -342,12 +347,12 @@ public function testReadWithInvalidLine()
 
         $caught = false;
         try {
-            $result = Reader::read(implode("\r\n", $data));
+            Reader::read(implode("\r\n", $data));
         } catch (ParseException $e) {
             $caught = true;
         }
 
-        $this->assertEquals(true, $caught);
+        self::assertEquals(true, $caught);
 
         $result = Reader::read(implode("\r\n", $data), Reader::OPTION_IGNORE_INVALID_LINES);
 
@@ -358,13 +363,13 @@ public function testReadWithInvalidLine()
             '',
         ]);
 
-        $this->assertEquals($expected, $result->serialize());
+        self::assertEquals($expected, $result->serialize());
     }
 
     /**
      * Reported as Issue 32.
      */
-    public function testReadIncompleteFile()
+    public function testReadIncompleteFile(): void
     {
         $this->expectException(ParseException::class);
         $input = <<<ICS
@@ -397,23 +402,23 @@ public function testReadIncompleteFile()
         Reader::read($input);
     }
 
-    public function testReadBrokenInput()
+    public function testReadBrokenInput(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         Reader::read(false);
     }
 
-    public function testReadBOM()
+    public function testReadBOM(): void
     {
-        $data = chr(0xef).chr(0xbb).chr(0xbf)."BEGIN:VCALENDAR\r\nEND:VCALENDAR";
+        $data = chr(0xEF).chr(0xBB).chr(0xBF)."BEGIN:VCALENDAR\r\nEND:VCALENDAR";
         $result = Reader::read($data);
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCALENDAR', $result->name);
-        $this->assertEquals(0, count($result->children()));
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCALENDAR', $result->name);
+        self::assertCount(0, $result->children());
     }
 
-    public function testReadXMLComponent()
+    public function testReadXMLComponent(): void
     {
         $data = <<<XML
 <?xml version="1.0" encoding="utf-8"?>
@@ -425,12 +430,12 @@ public function testReadXMLComponent()
 
         $result = Reader::readXML($data);
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCALENDAR', $result->name);
-        $this->assertEquals(0, count($result->children()));
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCALENDAR', $result->name);
+        self::assertCount(0, $result->children());
     }
 
-    public function testReadXMLStream()
+    public function testReadXMLStream(): void
     {
         $data = <<<XML
 <?xml version="1.0" encoding="utf-8"?>
@@ -446,12 +451,12 @@ public function testReadXMLStream()
 
         $result = Reader::readXML($stream);
 
-        $this->assertInstanceOf(Component::class, $result);
-        $this->assertEquals('VCALENDAR', $result->name);
-        $this->assertEquals(0, count($result->children()));
+        self::assertInstanceOf(Component::class, $result);
+        self::assertEquals('VCALENDAR', $result->name);
+        self::assertCount(0, $result->children());
     }
 
-    public function testReadDuplicateValue()
+    public function testReadDuplicateValue(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -472,6 +477,6 @@ public function testReadDuplicateValue()
 
         $result = Reader::read($input);
         $expected = "DTSTART;VALUE=DATE:20210818\r\n";
-        $this->assertSame($expected, $result->VEVENT->DTSTART->serialize());
+        self::assertSame($expected, $result->VEVENT->DTSTART->serialize());
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/ByMonthInDailyTest.php b/tests/VObject/Recur/EventIterator/ByMonthInDailyTest.php
index bd1eeb9b6..9b6b20df4 100644
--- a/tests/VObject/Recur/EventIterator/ByMonthInDailyTest.php
+++ b/tests/VObject/Recur/EventIterator/ByMonthInDailyTest.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Recur\EventIterator;
 
-use DateTime;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Reader;
@@ -12,7 +11,7 @@ class ByMonthInDailyTest extends TestCase
     /**
      * This tests the expansion of dates with DAILY frequency in RRULE with BYMONTH restrictions.
      */
-    public function testExpand()
+    public function testExpand(): void
     {
         $ics = <<<ICS
 BEGIN:VCALENDAR
@@ -37,9 +36,9 @@ public function testExpand()
 ICS;
 
         $vcal = Reader::read($ics);
-        $this->assertInstanceOf(VCalendar::class, $vcal);
+        self::assertInstanceOf(VCalendar::class, $vcal);
 
-        $vcal = $vcal->expand(new DateTime('2013-09-28'), new DateTime('2014-09-11'));
+        $vcal = $vcal->expand(new \DateTime('2013-09-28'), new \DateTime('2014-09-11'));
 
         $dates = [];
         foreach ($vcal->VEVENT as $event) {
@@ -55,6 +54,6 @@ public function testExpand()
             '20140907T160000Z',
         ];
 
-        $this->assertEquals($expectedDates, $dates, 'Recursed dates are restricted by month');
+        self::assertEquals($expectedDates, $dates, 'Recursed dates are restricted by month');
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/BySetPosHangTest.php b/tests/VObject/Recur/EventIterator/BySetPosHangTest.php
index 555f2ffd4..f5132e1d2 100644
--- a/tests/VObject/Recur/EventIterator/BySetPosHangTest.php
+++ b/tests/VObject/Recur/EventIterator/BySetPosHangTest.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Recur\EventIterator;
 
-use DateTime;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Reader;
@@ -15,7 +14,7 @@ class BySetPosHangTest extends TestCase
      *
      * See: https://github.com/fruux/sabre-vobject/issues/212
      */
-    public function testExpand()
+    public function testExpand(): void
     {
         $ics = <<<ICS
 BEGIN:VCALENDAR
@@ -32,9 +31,9 @@ public function testExpand()
 ICS;
 
         $vcal = Reader::read($ics);
-        $this->assertInstanceOf(VCalendar::class, $vcal);
+        self::assertInstanceOf(VCalendar::class, $vcal);
 
-        $vcal = $vcal->expand(new DateTime('2015-01-01'), new DateTime('2016-01-01'));
+        $vcal = $vcal->expand(new \DateTime('2015-01-01'), new \DateTime('2016-01-01'));
 
         $dates = [];
         foreach ($vcal->VEVENT as $event) {
@@ -57,6 +56,6 @@ public function testExpand()
             '20151224T160000Z',
         ];
 
-        $this->assertEquals($expectedDates, $dates);
+        self::assertEquals($expectedDates, $dates);
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/ExpandFloatingTimesTest.php b/tests/VObject/Recur/EventIterator/ExpandFloatingTimesTest.php
index 605e10dde..a7a39d1dd 100644
--- a/tests/VObject/Recur/EventIterator/ExpandFloatingTimesTest.php
+++ b/tests/VObject/Recur/EventIterator/ExpandFloatingTimesTest.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\Recur\EventIterator;
 
-use DateTime;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Reader;
@@ -12,7 +10,7 @@ class ExpandFloatingTimesTest extends TestCase
 {
     use \Sabre\VObject\PHPUnitAssertions;
 
-    public function testExpand()
+    public function testExpand(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -27,9 +25,9 @@ public function testExpand()
 ICS;
 
         $vcal = Reader::read($input);
-        $this->assertInstanceOf(VCalendar::class, $vcal);
+        self::assertInstanceOf(VCalendar::class, $vcal);
 
-        $vcal = $vcal->expand(new DateTime('2015-01-01'), new DateTime('2015-01-31'));
+        $vcal = $vcal->expand(new \DateTime('2015-01-01'), new \DateTime('2015-01-31'));
         $output = <<<ICS
 BEGIN:VCALENDAR
 VERSION:2.0
@@ -60,10 +58,10 @@ public function testExpand()
 END:VCALENDAR
 
 ICS;
-        $this->assertVObjectEqualsVObject($output, $vcal);
+        self::assertVObjectEqualsVObject($output, $vcal);
     }
 
-    public function testExpandWithReferenceTimezone()
+    public function testExpandWithReferenceTimezone(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -78,12 +76,12 @@ public function testExpandWithReferenceTimezone()
 ICS;
 
         $vcal = Reader::read($input);
-        $this->assertInstanceOf(VCalendar::class, $vcal);
+        self::assertInstanceOf(VCalendar::class, $vcal);
 
         $vcal = $vcal->expand(
-            new DateTime('2015-01-01'),
-            new DateTime('2015-01-31'),
-            new DateTimeZone('Europe/Berlin')
+            new \DateTime('2015-01-01'),
+            new \DateTime('2015-01-31'),
+            new \DateTimeZone('Europe/Berlin')
         );
 
         $output = <<<ICS
@@ -116,6 +114,6 @@ public function testExpandWithReferenceTimezone()
 END:VCALENDAR
 
 ICS;
-        $this->assertVObjectEqualsVObject($output, $vcal);
+        self::assertVObjectEqualsVObject($output, $vcal);
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/FifthTuesdayProblemTest.php b/tests/VObject/Recur/EventIterator/FifthTuesdayProblemTest.php
index 3db97ede2..8391a232a 100644
--- a/tests/VObject/Recur/EventIterator/FifthTuesdayProblemTest.php
+++ b/tests/VObject/Recur/EventIterator/FifthTuesdayProblemTest.php
@@ -14,7 +14,7 @@ class FifthTuesdayProblemTest extends TestCase
      *
      * @medium
      */
-    public function testGetDTEnd()
+    public function testGetDTEnd(): void
     {
         $ics = <<<ICS
 BEGIN:VCALENDAR
@@ -48,6 +48,6 @@ public function testGetDTEnd()
         // If we got here, it means we were successful. The bug that was in the
         // system before would fail on the 5th tuesday of the month, if the 5th
         // tuesday did not exist.
-        $this->assertTrue(true);
+        self::assertTrue(true);
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/HandleRDateExpandTest.php b/tests/VObject/Recur/EventIterator/HandleRDateExpandTest.php
index 548820191..4f434dd2a 100644
--- a/tests/VObject/Recur/EventIterator/HandleRDateExpandTest.php
+++ b/tests/VObject/Recur/EventIterator/HandleRDateExpandTest.php
@@ -2,19 +2,16 @@
 
 namespace Sabre\VObject\Recur\EventIterator;
 
-use DateTime;
-use DateTimeImmutable;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Reader;
 
 /**
- * This is a unittest for Issue #53.
+ * This is a unit test for Issue #53.
  */
 class HandleRDateExpandTest extends TestCase
 {
-    public function testExpand()
+    public function testExpand(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -37,24 +34,24 @@ public function testExpand()
 ICS;
 
         $vcal = Reader::read($input);
-        $this->assertInstanceOf(VCalendar::class, $vcal);
+        self::assertInstanceOf(VCalendar::class, $vcal);
 
-        $vcal = $vcal->expand(new DateTime('2015-01-01'), new DateTime('2015-12-01'));
+        $vcal = $vcal->expand(new \DateTime('2015-01-01'), new \DateTime('2015-12-01'));
 
         $result = iterator_to_array($vcal->VEVENT);
 
-        $this->assertEquals(5, count($result));
+        self::assertCount(5, $result);
 
-        $utc = new DateTimeZone('UTC');
+        $utc = new \DateTimeZone('UTC');
         $expected = [
-            new DateTimeImmutable('2015-10-12', $utc),
-            new DateTimeImmutable('2015-10-15', $utc),
-            new DateTimeImmutable('2015-10-17', $utc),
-            new DateTimeImmutable('2015-10-18', $utc),
-            new DateTimeImmutable('2015-10-20', $utc),
+            new \DateTimeImmutable('2015-10-12', $utc),
+            new \DateTimeImmutable('2015-10-15', $utc),
+            new \DateTimeImmutable('2015-10-17', $utc),
+            new \DateTimeImmutable('2015-10-18', $utc),
+            new \DateTimeImmutable('2015-10-20', $utc),
         ];
 
         $result = array_map(function ($ev) {return $ev->DTSTART->getDateTime(); }, $result);
-        $this->assertEquals($expected, $result);
+        self::assertEquals($expected, $result);
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/IncorrectExpandTest.php b/tests/VObject/Recur/EventIterator/IncorrectExpandTest.php
index f9fcda442..b0ecbbdbf 100644
--- a/tests/VObject/Recur/EventIterator/IncorrectExpandTest.php
+++ b/tests/VObject/Recur/EventIterator/IncorrectExpandTest.php
@@ -2,19 +2,18 @@
 
 namespace Sabre\VObject\Recur\EventIterator;
 
-use DateTime;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Reader;
 
 /**
- * This is a unittest for Issue #53.
+ * This is a unit test for Issue #53.
  */
 class IncorrectExpandTest extends TestCase
 {
     use \Sabre\VObject\PHPUnitAssertions;
 
-    public function testExpand()
+    public function testExpand(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -35,9 +34,9 @@ public function testExpand()
 ICS;
 
         $vcal = Reader::read($input);
-        $this->assertInstanceOf(VCalendar::class, $vcal);
+        self::assertInstanceOf(VCalendar::class, $vcal);
 
-        $vcal = $vcal->expand(new DateTime('2011-01-01'), new DateTime('2014-01-01'));
+        $vcal = $vcal->expand(new \DateTime('2011-01-01'), new \DateTime('2014-01-01'));
 
         $output = <<<ICS
 BEGIN:VCALENDAR
@@ -57,6 +56,6 @@ public function testExpand()
 END:VCALENDAR
 
 ICS;
-        $this->assertVObjectEqualsVObject($output, $vcal);
+        self::assertVObjectEqualsVObject($output, $vcal);
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/InfiniteLoopProblemTest.php b/tests/VObject/Recur/EventIterator/InfiniteLoopProblemTest.php
index 5546c508d..591140e6d 100644
--- a/tests/VObject/Recur/EventIterator/InfiniteLoopProblemTest.php
+++ b/tests/VObject/Recur/EventIterator/InfiniteLoopProblemTest.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\Recur\EventIterator;
 
-use DateTimeImmutable;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\InvalidDataException;
@@ -11,8 +9,7 @@
 
 class InfiniteLoopProblemTest extends TestCase
 {
-    /** @var VCalendar */
-    private $vcal;
+    private VCalendar $vcal;
 
     public function setUp(): void
     {
@@ -23,20 +20,20 @@ public function setUp(): void
      * This bug came from a Fruux customer. This would result in a never-ending
      * request.
      */
-    public function testFastForwardTooFar()
+    public function testFastForwardTooFar(): void
     {
         $ev = $this->vcal->createComponent('VEVENT');
         $ev->UID = 'foobar';
         $ev->DTSTART = '20090420T180000Z';
         $ev->RRULE = 'FREQ=WEEKLY;BYDAY=MO;UNTIL=20090704T205959Z;INTERVAL=1';
 
-        $this->assertFalse($ev->isInTimeRange(new DateTimeImmutable('2012-01-01 12:00:00'), new DateTimeImmutable('3000-01-01 00:00:00')));
+        self::assertFalse($ev->isInTimeRange(new \DateTimeImmutable('2012-01-01 12:00:00'), new \DateTimeImmutable('3000-01-01 00:00:00')));
     }
 
     /**
      * Different bug, also likely an infinite loop.
      */
-    public function testYearlyByMonthLoop()
+    public function testYearlyByMonthLoop(): void
     {
         $ev = $this->vcal->createComponent('VEVENT');
         $ev->UID = 'uuid';
@@ -55,20 +52,20 @@ public function testYearlyByMonthLoop()
         $this->vcal->add($ev);
 
         $it = new Recur\EventIterator($this->vcal, 'uuid');
-        $it->fastForward(new DateTimeImmutable('2012-01-29 23:00:00', new DateTimeZone('UTC')));
+        $it->fastForward(new \DateTimeImmutable('2012-01-29 23:00:00', new \DateTimeZone('UTC')));
 
         $collect = [];
 
         while ($it->valid()) {
             $collect[] = $it->getDtStart();
-            if ($it->getDtStart() > new DateTimeImmutable('2013-02-05 22:59:59', new DateTimeZone('UTC'))) {
+            if ($it->getDtStart() > new \DateTimeImmutable('2013-02-05 22:59:59', new \DateTimeZone('UTC'))) {
                 break;
             }
             $it->next();
         }
 
-        $this->assertEquals(
-            [new DateTimeImmutable('2012-02-01 15:45:00', new DateTimeZone('Europe/Berlin'))],
+        self::assertEquals(
+            [new \DateTimeImmutable('2012-02-01 15:45:00', new \DateTimeZone('Europe/Berlin'))],
             $collect
         );
     }
@@ -78,7 +75,7 @@ public function testYearlyByMonthLoop()
      * this means we increase the current day (or week, month) by 0, this also
      * results in an infinite loop.
      */
-    public function testZeroInterval()
+    public function testZeroInterval(): void
     {
         $this->expectException(InvalidDataException::class);
         $ev = $this->vcal->createComponent('VEVENT');
@@ -88,8 +85,8 @@ public function testZeroInterval()
         $this->vcal->add($ev);
 
         $it = new Recur\EventIterator($this->vcal, 'uuid');
-        $it->fastForward(new DateTimeImmutable('2013-01-01 23:00:00', new DateTimeZone('UTC')));
+        $it->fastForward(new \DateTimeImmutable('2013-01-01 23:00:00', new \DateTimeZone('UTC')));
 
-        // if we got this far.. it means we are no longer infinitely looping
+        // if we got this far it means we are no longer infinitely looping
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/Issue26Test.php b/tests/VObject/Recur/EventIterator/Issue26Test.php
index 3313c3ec6..06cd63883 100644
--- a/tests/VObject/Recur/EventIterator/Issue26Test.php
+++ b/tests/VObject/Recur/EventIterator/Issue26Test.php
@@ -10,7 +10,7 @@
 
 class Issue26Test extends TestCase
 {
-    public function testExpand()
+    public function testExpand(): void
     {
         $this->expectException(InvalidDataException::class);
         $input = <<<ICS
@@ -26,8 +26,8 @@ public function testExpand()
 ICS;
 
         $vcal = Reader::read($input);
-        $this->assertInstanceOf(VCalendar::class, $vcal);
+        self::assertInstanceOf(VCalendar::class, $vcal);
 
-        $it = new EventIterator($vcal, 'bae5d57a98');
+        new EventIterator($vcal, 'bae5d57a98');
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/Issue48Test.php b/tests/VObject/Recur/EventIterator/Issue48Test.php
index aef592590..d2b809365 100644
--- a/tests/VObject/Recur/EventIterator/Issue48Test.php
+++ b/tests/VObject/Recur/EventIterator/Issue48Test.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\Recur\EventIterator;
 
-use DateTimeImmutable;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Reader;
@@ -11,7 +9,7 @@
 
 class Issue48Test extends TestCase
 {
-    public function testExpand()
+    public function testExpand(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -31,20 +29,20 @@ public function testExpand()
 ICS;
 
         $vcal = Reader::read($input);
-        $this->assertInstanceOf(VCalendar::class, $vcal);
+        self::assertInstanceOf(VCalendar::class, $vcal);
 
         $it = new EventIterator($vcal, 'foo');
 
         $result = iterator_to_array($it);
 
-        $tz = new DateTimeZone('Europe/Moscow');
+        $tz = new \DateTimeZone('Europe/Moscow');
 
         $expected = [
-            new DateTimeImmutable('2013-07-10 11:00:00', $tz),
-            new DateTimeImmutable('2013-07-12 11:00:00', $tz),
-            new DateTimeImmutable('2013-07-13 11:00:00', $tz),
+            new \DateTimeImmutable('2013-07-10 11:00:00', $tz),
+            new \DateTimeImmutable('2013-07-12 11:00:00', $tz),
+            new \DateTimeImmutable('2013-07-13 11:00:00', $tz),
         ];
 
-        $this->assertEquals($expected, $result);
+        self::assertEquals($expected, $result);
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/Issue50Test.php b/tests/VObject/Recur/EventIterator/Issue50Test.php
index 5c476e6f2..ec05de1b1 100644
--- a/tests/VObject/Recur/EventIterator/Issue50Test.php
+++ b/tests/VObject/Recur/EventIterator/Issue50Test.php
@@ -2,8 +2,6 @@
 
 namespace Sabre\VObject\Recur\EventIterator;
 
-use DateTimeImmutable;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Reader;
@@ -11,7 +9,7 @@
 
 class Issue50Test extends TestCase
 {
-    public function testExpand()
+    public function testExpand(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -105,7 +103,7 @@ public function testExpand()
 ICS;
 
         $vcal = Reader::read($input);
-        $this->assertInstanceOf(VCalendar::class, $vcal);
+        self::assertInstanceOf(VCalendar::class, $vcal);
 
         $it = new EventIterator($vcal, '1aef0b27-3d92-4581-829a-11999dd36724');
 
@@ -114,14 +112,14 @@ public function testExpand()
             $result[] = $instance;
         }
 
-        $tz = new DateTimeZone('Europe/Brussels');
+        $tz = new \DateTimeZone('Europe/Brussels');
 
-        $this->assertEquals([
-            new DateTimeImmutable('2013-07-15 09:00:00', $tz),
-            new DateTimeImmutable('2013-07-16 07:00:00', $tz),
-            new DateTimeImmutable('2013-07-17 07:00:00', $tz),
-            new DateTimeImmutable('2013-07-18 09:00:00', $tz),
-            new DateTimeImmutable('2013-07-19 07:00:00', $tz),
+        self::assertEquals([
+            new \DateTimeImmutable('2013-07-15 09:00:00', $tz),
+            new \DateTimeImmutable('2013-07-16 07:00:00', $tz),
+            new \DateTimeImmutable('2013-07-17 07:00:00', $tz),
+            new \DateTimeImmutable('2013-07-18 09:00:00', $tz),
+            new \DateTimeImmutable('2013-07-19 07:00:00', $tz),
         ], $result);
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/MainTest.php b/tests/VObject/Recur/EventIterator/MainTest.php
index 9350080e4..022df4a3b 100644
--- a/tests/VObject/Recur/EventIterator/MainTest.php
+++ b/tests/VObject/Recur/EventIterator/MainTest.php
@@ -2,23 +2,32 @@
 
 namespace Sabre\VObject\Recur\EventIterator;
 
-use DateTimeImmutable;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component\VCalendar;
+use Sabre\VObject\Component\VEvent;
 use Sabre\VObject\InvalidDataException;
+use Sabre\VObject\Property\ICalendar\DateTime;
 use Sabre\VObject\Recur\EventIterator;
+use Sabre\VObject\Recur\MaxInstancesExceededException;
+use Sabre\VObject\Recur\NoInstancesException;
 
 class MainTest extends TestCase
 {
-    public function testValues()
+    /**
+     * @throws MaxInstancesExceededException
+     * @throws NoInstancesException
+     * @throws InvalidDataException
+     */
+    public function testValues(): void
     {
         $vcal = new VCalendar();
+        /** @var VEvent $ev */
         $ev = $vcal->createComponent('VEVENT');
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=DAILY;BYHOUR=10;BYMINUTE=5;BYSECOND=16';
+        /** @var DateTime $dtStart */
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-10-07'));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-10-07'));
 
         $ev->add($dtStart);
 
@@ -26,54 +35,73 @@ public function testValues()
 
         $it = new EventIterator($vcal, (string) $ev->UID);
 
-        $this->assertTrue($it->isInfinite());
+        self::assertTrue($it->isInfinite());
     }
 
     /**
      * @depends testValues
+     *
+     * @throws \Exception
      */
-    public function testInvalidFreq()
+    public function testInvalidFreq(): void
     {
         $this->expectException(InvalidDataException::class);
         $vcal = new VCalendar();
+        /** @var VEvent $ev */
         $ev = $vcal->createComponent('VEVENT');
         $ev->RRULE = 'FREQ=SMONTHLY;INTERVAL=3;UNTIL=20111025T000000Z';
         $ev->UID = 'foo';
+        /** @var DateTime $dtStart */
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-10-07', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-10-07', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        new EventIterator($vcal, (string) $ev->UID);
     }
 
-    public function testVCalendarNoUID()
+    /**
+     * @throws MaxInstancesExceededException
+     * @throws InvalidDataException
+     * @throws NoInstancesException
+     */
+    public function testVCalendarNoUID(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $vcal = new VCalendar();
-        $it = new EventIterator($vcal);
+        new EventIterator($vcal);
     }
 
-    public function testVCalendarInvalidUID()
+    /**
+     * @throws MaxInstancesExceededException
+     * @throws NoInstancesException
+     * @throws InvalidDataException
+     */
+    public function testVCalendarInvalidUID(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $vcal = new VCalendar();
-        $it = new EventIterator($vcal, 'foo');
+        new EventIterator($vcal, 'foo');
     }
 
     /**
      * @depends testValues
+     *
+     * @throws InvalidDataException
+     * @throws \Exception
      */
-    public function testHourly()
+    public function testHourly(): void
     {
         $vcal = new VCalendar();
+        /** @var VEvent $ev */
         $ev = $vcal->createComponent('VEVENT');
 
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=HOURLY;INTERVAL=3;UNTIL=20111025T000000Z';
+        /** @var DateTime $dtStart */
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-10-07 12:00:00', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-10-07 12:00:00', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
         $vcal->add($ev);
@@ -92,22 +120,22 @@ public function testHourly()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-10-07 12:00:00', $tz),
-                new DateTimeImmutable('2011-10-07 15:00:00', $tz),
-                new DateTimeImmutable('2011-10-07 18:00:00', $tz),
-                new DateTimeImmutable('2011-10-07 21:00:00', $tz),
-                new DateTimeImmutable('2011-10-08 00:00:00', $tz),
-                new DateTimeImmutable('2011-10-08 03:00:00', $tz),
-                new DateTimeImmutable('2011-10-08 06:00:00', $tz),
-                new DateTimeImmutable('2011-10-08 09:00:00', $tz),
-                new DateTimeImmutable('2011-10-08 12:00:00', $tz),
-                new DateTimeImmutable('2011-10-08 15:00:00', $tz),
-                new DateTimeImmutable('2011-10-08 18:00:00', $tz),
-                new DateTimeImmutable('2011-10-08 21:00:00', $tz),
+                new \DateTimeImmutable('2011-10-07 12:00:00', $tz),
+                new \DateTimeImmutable('2011-10-07 15:00:00', $tz),
+                new \DateTimeImmutable('2011-10-07 18:00:00', $tz),
+                new \DateTimeImmutable('2011-10-07 21:00:00', $tz),
+                new \DateTimeImmutable('2011-10-08 00:00:00', $tz),
+                new \DateTimeImmutable('2011-10-08 03:00:00', $tz),
+                new \DateTimeImmutable('2011-10-08 06:00:00', $tz),
+                new \DateTimeImmutable('2011-10-08 09:00:00', $tz),
+                new \DateTimeImmutable('2011-10-08 12:00:00', $tz),
+                new \DateTimeImmutable('2011-10-08 15:00:00', $tz),
+                new \DateTimeImmutable('2011-10-08 18:00:00', $tz),
+                new \DateTimeImmutable('2011-10-08 21:00:00', $tz),
             ],
             $result
         );
@@ -115,16 +143,23 @@ public function testHourly()
 
     /**
      * @depends testValues
+     *
+     * @throws InvalidDataException
+     * @throws MaxInstancesExceededException
+     * @throws NoInstancesException
+     * @throws \Exception
      */
-    public function testDaily()
+    public function testDaily(): void
     {
         $vcal = new VCalendar();
+        /** @var VEvent $ev */
         $ev = $vcal->createComponent('VEVENT');
 
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=DAILY;INTERVAL=3;UNTIL=20111025T000000Z';
+        /** @var DateTime $dtStart */
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-10-07', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-10-07', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -144,17 +179,17 @@ public function testDaily()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-10-07', $tz),
-                new DateTimeImmutable('2011-10-10', $tz),
-                new DateTimeImmutable('2011-10-13', $tz),
-                new DateTimeImmutable('2011-10-16', $tz),
-                new DateTimeImmutable('2011-10-19', $tz),
-                new DateTimeImmutable('2011-10-22', $tz),
-                new DateTimeImmutable('2011-10-25', $tz),
+                new \DateTimeImmutable('2011-10-07', $tz),
+                new \DateTimeImmutable('2011-10-10', $tz),
+                new \DateTimeImmutable('2011-10-13', $tz),
+                new \DateTimeImmutable('2011-10-16', $tz),
+                new \DateTimeImmutable('2011-10-19', $tz),
+                new \DateTimeImmutable('2011-10-22', $tz),
+                new \DateTimeImmutable('2011-10-25', $tz),
             ],
             $result
         );
@@ -163,14 +198,14 @@ public function testDaily()
     /**
      * @depends testValues
      */
-    public function testNoRRULE()
+    public function testNoRRULE(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
 
         $ev->UID = 'bla';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-10-07', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-10-07', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -190,11 +225,11 @@ public function testNoRRULE()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-10-07', $tz),
+                new \DateTimeImmutable('2011-10-07', $tz),
             ],
             $result
         );
@@ -203,7 +238,7 @@ public function testNoRRULE()
     /**
      * @depends testValues
      */
-    public function testDailyByDayByHour()
+    public function testDailyByDayByHour(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -211,7 +246,7 @@ public function testDailyByDayByHour()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=DAILY;BYDAY=SA,SU;BYHOUR=6,7';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-10-08 06:00:00', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-10-08 06:00:00', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -231,22 +266,22 @@ public function testDailyByDayByHour()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-10-08 06:00:00', $tz),
-                new DateTimeImmutable('2011-10-08 07:00:00', $tz),
-                new DateTimeImmutable('2011-10-09 06:00:00', $tz),
-                new DateTimeImmutable('2011-10-09 07:00:00', $tz),
-                new DateTimeImmutable('2011-10-15 06:00:00', $tz),
-                new DateTimeImmutable('2011-10-15 07:00:00', $tz),
-                new DateTimeImmutable('2011-10-16 06:00:00', $tz),
-                new DateTimeImmutable('2011-10-16 07:00:00', $tz),
-                new DateTimeImmutable('2011-10-22 06:00:00', $tz),
-                new DateTimeImmutable('2011-10-22 07:00:00', $tz),
-                new DateTimeImmutable('2011-10-23 06:00:00', $tz),
-                new DateTimeImmutable('2011-10-23 07:00:00', $tz),
+                new \DateTimeImmutable('2011-10-08 06:00:00', $tz),
+                new \DateTimeImmutable('2011-10-08 07:00:00', $tz),
+                new \DateTimeImmutable('2011-10-09 06:00:00', $tz),
+                new \DateTimeImmutable('2011-10-09 07:00:00', $tz),
+                new \DateTimeImmutable('2011-10-15 06:00:00', $tz),
+                new \DateTimeImmutable('2011-10-15 07:00:00', $tz),
+                new \DateTimeImmutable('2011-10-16 06:00:00', $tz),
+                new \DateTimeImmutable('2011-10-16 07:00:00', $tz),
+                new \DateTimeImmutable('2011-10-22 06:00:00', $tz),
+                new \DateTimeImmutable('2011-10-22 07:00:00', $tz),
+                new \DateTimeImmutable('2011-10-23 06:00:00', $tz),
+                new \DateTimeImmutable('2011-10-23 07:00:00', $tz),
             ],
             $result
         );
@@ -255,7 +290,7 @@ public function testDailyByDayByHour()
     /**
      * @depends testValues
      */
-    public function testDailyByHour()
+    public function testDailyByHour(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -263,7 +298,7 @@ public function testDailyByHour()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=DAILY;INTERVAL=2;BYHOUR=10,11,12,13,14,15';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2012-10-11 12:00:00', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2012-10-11 12:00:00', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -283,22 +318,22 @@ public function testDailyByHour()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2012-10-11 12:00:00', $tz),
-                new DateTimeImmutable('2012-10-11 13:00:00', $tz),
-                new DateTimeImmutable('2012-10-11 14:00:00', $tz),
-                new DateTimeImmutable('2012-10-11 15:00:00', $tz),
-                new DateTimeImmutable('2012-10-13 10:00:00', $tz),
-                new DateTimeImmutable('2012-10-13 11:00:00', $tz),
-                new DateTimeImmutable('2012-10-13 12:00:00', $tz),
-                new DateTimeImmutable('2012-10-13 13:00:00', $tz),
-                new DateTimeImmutable('2012-10-13 14:00:00', $tz),
-                new DateTimeImmutable('2012-10-13 15:00:00', $tz),
-                new DateTimeImmutable('2012-10-15 10:00:00', $tz),
-                new DateTimeImmutable('2012-10-15 11:00:00', $tz),
+                new \DateTimeImmutable('2012-10-11 12:00:00', $tz),
+                new \DateTimeImmutable('2012-10-11 13:00:00', $tz),
+                new \DateTimeImmutable('2012-10-11 14:00:00', $tz),
+                new \DateTimeImmutable('2012-10-11 15:00:00', $tz),
+                new \DateTimeImmutable('2012-10-13 10:00:00', $tz),
+                new \DateTimeImmutable('2012-10-13 11:00:00', $tz),
+                new \DateTimeImmutable('2012-10-13 12:00:00', $tz),
+                new \DateTimeImmutable('2012-10-13 13:00:00', $tz),
+                new \DateTimeImmutable('2012-10-13 14:00:00', $tz),
+                new \DateTimeImmutable('2012-10-13 15:00:00', $tz),
+                new \DateTimeImmutable('2012-10-15 10:00:00', $tz),
+                new \DateTimeImmutable('2012-10-15 11:00:00', $tz),
             ],
             $result
         );
@@ -307,7 +342,7 @@ public function testDailyByHour()
     /**
      * @depends testValues
      */
-    public function testDailyByDay()
+    public function testDailyByDay(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -315,7 +350,7 @@ public function testDailyByDay()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=DAILY;INTERVAL=2;BYDAY=TU,WE,FR';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-10-07', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-10-07', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -335,22 +370,22 @@ public function testDailyByDay()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-10-07', $tz),
-                new DateTimeImmutable('2011-10-11', $tz),
-                new DateTimeImmutable('2011-10-19', $tz),
-                new DateTimeImmutable('2011-10-21', $tz),
-                new DateTimeImmutable('2011-10-25', $tz),
-                new DateTimeImmutable('2011-11-02', $tz),
-                new DateTimeImmutable('2011-11-04', $tz),
-                new DateTimeImmutable('2011-11-08', $tz),
-                new DateTimeImmutable('2011-11-16', $tz),
-                new DateTimeImmutable('2011-11-18', $tz),
-                new DateTimeImmutable('2011-11-22', $tz),
-                new DateTimeImmutable('2011-11-30', $tz),
+                new \DateTimeImmutable('2011-10-07', $tz),
+                new \DateTimeImmutable('2011-10-11', $tz),
+                new \DateTimeImmutable('2011-10-19', $tz),
+                new \DateTimeImmutable('2011-10-21', $tz),
+                new \DateTimeImmutable('2011-10-25', $tz),
+                new \DateTimeImmutable('2011-11-02', $tz),
+                new \DateTimeImmutable('2011-11-04', $tz),
+                new \DateTimeImmutable('2011-11-08', $tz),
+                new \DateTimeImmutable('2011-11-16', $tz),
+                new \DateTimeImmutable('2011-11-18', $tz),
+                new \DateTimeImmutable('2011-11-22', $tz),
+                new \DateTimeImmutable('2011-11-30', $tz),
             ],
             $result
         );
@@ -359,7 +394,7 @@ public function testDailyByDay()
     /**
      * @depends testValues
      */
-    public function testWeekly()
+    public function testWeekly(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -367,7 +402,7 @@ public function testWeekly()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=WEEKLY;INTERVAL=2;COUNT=10';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-10-07', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-10-07', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -387,20 +422,20 @@ public function testWeekly()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-10-07', $tz),
-                new DateTimeImmutable('2011-10-21', $tz),
-                new DateTimeImmutable('2011-11-04', $tz),
-                new DateTimeImmutable('2011-11-18', $tz),
-                new DateTimeImmutable('2011-12-02', $tz),
-                new DateTimeImmutable('2011-12-16', $tz),
-                new DateTimeImmutable('2011-12-30', $tz),
-                new DateTimeImmutable('2012-01-13', $tz),
-                new DateTimeImmutable('2012-01-27', $tz),
-                new DateTimeImmutable('2012-02-10', $tz),
+                new \DateTimeImmutable('2011-10-07', $tz),
+                new \DateTimeImmutable('2011-10-21', $tz),
+                new \DateTimeImmutable('2011-11-04', $tz),
+                new \DateTimeImmutable('2011-11-18', $tz),
+                new \DateTimeImmutable('2011-12-02', $tz),
+                new \DateTimeImmutable('2011-12-16', $tz),
+                new \DateTimeImmutable('2011-12-30', $tz),
+                new \DateTimeImmutable('2012-01-13', $tz),
+                new \DateTimeImmutable('2012-01-27', $tz),
+                new \DateTimeImmutable('2012-02-10', $tz),
             ],
             $result
         );
@@ -409,7 +444,7 @@ public function testWeekly()
     /**
      * @depends testValues
      */
-    public function testWeeklyByDayByHour()
+    public function testWeeklyByDayByHour(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -417,7 +452,7 @@ public function testWeeklyByDayByHour()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=WEEKLY;INTERVAL=2;BYDAY=TU,WE,FR;WKST=MO;BYHOUR=8,9,10';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-10-07 08:00:00', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-10-07 08:00:00', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -437,25 +472,25 @@ public function testWeeklyByDayByHour()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-10-07 08:00:00', $tz),
-                new DateTimeImmutable('2011-10-07 09:00:00', $tz),
-                new DateTimeImmutable('2011-10-07 10:00:00', $tz),
-                new DateTimeImmutable('2011-10-18 08:00:00', $tz),
-                new DateTimeImmutable('2011-10-18 09:00:00', $tz),
-                new DateTimeImmutable('2011-10-18 10:00:00', $tz),
-                new DateTimeImmutable('2011-10-19 08:00:00', $tz),
-                new DateTimeImmutable('2011-10-19 09:00:00', $tz),
-                new DateTimeImmutable('2011-10-19 10:00:00', $tz),
-                new DateTimeImmutable('2011-10-21 08:00:00', $tz),
-                new DateTimeImmutable('2011-10-21 09:00:00', $tz),
-                new DateTimeImmutable('2011-10-21 10:00:00', $tz),
-                new DateTimeImmutable('2011-11-01 08:00:00', $tz),
-                new DateTimeImmutable('2011-11-01 09:00:00', $tz),
-                new DateTimeImmutable('2011-11-01 10:00:00', $tz),
+                new \DateTimeImmutable('2011-10-07 08:00:00', $tz),
+                new \DateTimeImmutable('2011-10-07 09:00:00', $tz),
+                new \DateTimeImmutable('2011-10-07 10:00:00', $tz),
+                new \DateTimeImmutable('2011-10-18 08:00:00', $tz),
+                new \DateTimeImmutable('2011-10-18 09:00:00', $tz),
+                new \DateTimeImmutable('2011-10-18 10:00:00', $tz),
+                new \DateTimeImmutable('2011-10-19 08:00:00', $tz),
+                new \DateTimeImmutable('2011-10-19 09:00:00', $tz),
+                new \DateTimeImmutable('2011-10-19 10:00:00', $tz),
+                new \DateTimeImmutable('2011-10-21 08:00:00', $tz),
+                new \DateTimeImmutable('2011-10-21 09:00:00', $tz),
+                new \DateTimeImmutable('2011-10-21 10:00:00', $tz),
+                new \DateTimeImmutable('2011-11-01 08:00:00', $tz),
+                new \DateTimeImmutable('2011-11-01 09:00:00', $tz),
+                new \DateTimeImmutable('2011-11-01 10:00:00', $tz),
             ],
             $result
         );
@@ -464,7 +499,7 @@ public function testWeeklyByDayByHour()
     /**
      * @depends testValues
      */
-    public function testWeeklyByDaySpecificHour()
+    public function testWeeklyByDaySpecificHour(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -472,7 +507,7 @@ public function testWeeklyByDaySpecificHour()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=WEEKLY;INTERVAL=2;BYDAY=TU,WE,FR;WKST=SU';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-10-07 18:00:00', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-10-07 18:00:00', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -492,22 +527,22 @@ public function testWeeklyByDaySpecificHour()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-10-07 18:00:00', $tz),
-                new DateTimeImmutable('2011-10-18 18:00:00', $tz),
-                new DateTimeImmutable('2011-10-19 18:00:00', $tz),
-                new DateTimeImmutable('2011-10-21 18:00:00', $tz),
-                new DateTimeImmutable('2011-11-01 18:00:00', $tz),
-                new DateTimeImmutable('2011-11-02 18:00:00', $tz),
-                new DateTimeImmutable('2011-11-04 18:00:00', $tz),
-                new DateTimeImmutable('2011-11-15 18:00:00', $tz),
-                new DateTimeImmutable('2011-11-16 18:00:00', $tz),
-                new DateTimeImmutable('2011-11-18 18:00:00', $tz),
-                new DateTimeImmutable('2011-11-29 18:00:00', $tz),
-                new DateTimeImmutable('2011-11-30 18:00:00', $tz),
+                new \DateTimeImmutable('2011-10-07 18:00:00', $tz),
+                new \DateTimeImmutable('2011-10-18 18:00:00', $tz),
+                new \DateTimeImmutable('2011-10-19 18:00:00', $tz),
+                new \DateTimeImmutable('2011-10-21 18:00:00', $tz),
+                new \DateTimeImmutable('2011-11-01 18:00:00', $tz),
+                new \DateTimeImmutable('2011-11-02 18:00:00', $tz),
+                new \DateTimeImmutable('2011-11-04 18:00:00', $tz),
+                new \DateTimeImmutable('2011-11-15 18:00:00', $tz),
+                new \DateTimeImmutable('2011-11-16 18:00:00', $tz),
+                new \DateTimeImmutable('2011-11-18 18:00:00', $tz),
+                new \DateTimeImmutable('2011-11-29 18:00:00', $tz),
+                new \DateTimeImmutable('2011-11-30 18:00:00', $tz),
             ],
             $result
         );
@@ -516,7 +551,7 @@ public function testWeeklyByDaySpecificHour()
     /**
      * @depends testValues
      */
-    public function testWeeklyByDay()
+    public function testWeeklyByDay(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -524,7 +559,7 @@ public function testWeeklyByDay()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=WEEKLY;INTERVAL=2;BYDAY=TU,WE,FR;WKST=SU';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-10-07', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-10-07', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -544,22 +579,22 @@ public function testWeeklyByDay()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-10-07', $tz),
-                new DateTimeImmutable('2011-10-18', $tz),
-                new DateTimeImmutable('2011-10-19', $tz),
-                new DateTimeImmutable('2011-10-21', $tz),
-                new DateTimeImmutable('2011-11-01', $tz),
-                new DateTimeImmutable('2011-11-02', $tz),
-                new DateTimeImmutable('2011-11-04', $tz),
-                new DateTimeImmutable('2011-11-15', $tz),
-                new DateTimeImmutable('2011-11-16', $tz),
-                new DateTimeImmutable('2011-11-18', $tz),
-                new DateTimeImmutable('2011-11-29', $tz),
-                new DateTimeImmutable('2011-11-30', $tz),
+                new \DateTimeImmutable('2011-10-07', $tz),
+                new \DateTimeImmutable('2011-10-18', $tz),
+                new \DateTimeImmutable('2011-10-19', $tz),
+                new \DateTimeImmutable('2011-10-21', $tz),
+                new \DateTimeImmutable('2011-11-01', $tz),
+                new \DateTimeImmutable('2011-11-02', $tz),
+                new \DateTimeImmutable('2011-11-04', $tz),
+                new \DateTimeImmutable('2011-11-15', $tz),
+                new \DateTimeImmutable('2011-11-16', $tz),
+                new \DateTimeImmutable('2011-11-18', $tz),
+                new \DateTimeImmutable('2011-11-29', $tz),
+                new \DateTimeImmutable('2011-11-30', $tz),
             ],
             $result
         );
@@ -568,7 +603,7 @@ public function testWeeklyByDay()
     /**
      * @depends testValues
      */
-    public function testMonthly()
+    public function testMonthly(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -576,7 +611,7 @@ public function testMonthly()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=MONTHLY;INTERVAL=3;COUNT=5';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-12-05', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-12-05', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -595,15 +630,15 @@ public function testMonthly()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-12-05', $tz),
-                new DateTimeImmutable('2012-03-05', $tz),
-                new DateTimeImmutable('2012-06-05', $tz),
-                new DateTimeImmutable('2012-09-05', $tz),
-                new DateTimeImmutable('2012-12-05', $tz),
+                new \DateTimeImmutable('2011-12-05', $tz),
+                new \DateTimeImmutable('2012-03-05', $tz),
+                new \DateTimeImmutable('2012-06-05', $tz),
+                new \DateTimeImmutable('2012-09-05', $tz),
+                new \DateTimeImmutable('2012-12-05', $tz),
             ],
             $result
         );
@@ -612,7 +647,7 @@ public function testMonthly()
     /**
      * @depends testValues
      */
-    public function testMonthlyEndOfMonth()
+    public function testMonthlyEndOfMonth(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -620,7 +655,7 @@ public function testMonthlyEndOfMonth()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=MONTHLY;INTERVAL=2;COUNT=12';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-12-31', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-12-31', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -639,22 +674,22 @@ public function testMonthlyEndOfMonth()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-12-31', $tz),
-                new DateTimeImmutable('2012-08-31', $tz),
-                new DateTimeImmutable('2012-10-31', $tz),
-                new DateTimeImmutable('2012-12-31', $tz),
-                new DateTimeImmutable('2013-08-31', $tz),
-                new DateTimeImmutable('2013-10-31', $tz),
-                new DateTimeImmutable('2013-12-31', $tz),
-                new DateTimeImmutable('2014-08-31', $tz),
-                new DateTimeImmutable('2014-10-31', $tz),
-                new DateTimeImmutable('2014-12-31', $tz),
-                new DateTimeImmutable('2015-08-31', $tz),
-                new DateTimeImmutable('2015-10-31', $tz),
+                new \DateTimeImmutable('2011-12-31', $tz),
+                new \DateTimeImmutable('2012-08-31', $tz),
+                new \DateTimeImmutable('2012-10-31', $tz),
+                new \DateTimeImmutable('2012-12-31', $tz),
+                new \DateTimeImmutable('2013-08-31', $tz),
+                new \DateTimeImmutable('2013-10-31', $tz),
+                new \DateTimeImmutable('2013-12-31', $tz),
+                new \DateTimeImmutable('2014-08-31', $tz),
+                new \DateTimeImmutable('2014-10-31', $tz),
+                new \DateTimeImmutable('2014-12-31', $tz),
+                new \DateTimeImmutable('2015-08-31', $tz),
+                new \DateTimeImmutable('2015-10-31', $tz),
             ],
             $result
         );
@@ -662,16 +697,23 @@ public function testMonthlyEndOfMonth()
 
     /**
      * @depends testValues
+     *
+     * @throws InvalidDataException
+     * @throws MaxInstancesExceededException
+     * @throws NoInstancesException
+     * @throws \Exception
      */
-    public function testMonthlyByMonthDay()
+    public function testMonthlyByMonthDay(): void
     {
         $vcal = new VCalendar();
+        /** @var VEvent $ev */
         $ev = $vcal->createComponent('VEVENT');
 
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=MONTHLY;INTERVAL=5;COUNT=9;BYMONTHDAY=1,31,-7';
+        /** @var DateTime $dtStart */
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-01-01', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-01-01', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -690,19 +732,19 @@ public function testMonthlyByMonthDay()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-01-01', $tz),
-                new DateTimeImmutable('2011-01-25', $tz),
-                new DateTimeImmutable('2011-01-31', $tz),
-                new DateTimeImmutable('2011-06-01', $tz),
-                new DateTimeImmutable('2011-06-24', $tz),
-                new DateTimeImmutable('2011-11-01', $tz),
-                new DateTimeImmutable('2011-11-24', $tz),
-                new DateTimeImmutable('2012-04-01', $tz),
-                new DateTimeImmutable('2012-04-24', $tz),
+                new \DateTimeImmutable('2011-01-01', $tz),
+                new \DateTimeImmutable('2011-01-25', $tz),
+                new \DateTimeImmutable('2011-01-31', $tz),
+                new \DateTimeImmutable('2011-06-01', $tz),
+                new \DateTimeImmutable('2011-06-24', $tz),
+                new \DateTimeImmutable('2011-11-01', $tz),
+                new \DateTimeImmutable('2011-11-24', $tz),
+                new \DateTimeImmutable('2012-04-01', $tz),
+                new \DateTimeImmutable('2012-04-24', $tz),
             ],
             $result
         );
@@ -713,9 +755,10 @@ public function testMonthlyByMonthDay()
      * after 1 second. Would be good to optimize later.
      *
      * @depends testValues
+     *
      * @medium
      */
-    public function testMonthlyByDay()
+    public function testMonthlyByDay(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -723,7 +766,7 @@ public function testMonthlyByDay()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=MONTHLY;INTERVAL=2;COUNT=16;BYDAY=MO,-2TU,+1WE,3TH';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-01-03', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-01-03', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -742,26 +785,26 @@ public function testMonthlyByDay()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-01-03', $tz),
-                new DateTimeImmutable('2011-01-05', $tz),
-                new DateTimeImmutable('2011-01-10', $tz),
-                new DateTimeImmutable('2011-01-17', $tz),
-                new DateTimeImmutable('2011-01-18', $tz),
-                new DateTimeImmutable('2011-01-20', $tz),
-                new DateTimeImmutable('2011-01-24', $tz),
-                new DateTimeImmutable('2011-01-31', $tz),
-                new DateTimeImmutable('2011-03-02', $tz),
-                new DateTimeImmutable('2011-03-07', $tz),
-                new DateTimeImmutable('2011-03-14', $tz),
-                new DateTimeImmutable('2011-03-17', $tz),
-                new DateTimeImmutable('2011-03-21', $tz),
-                new DateTimeImmutable('2011-03-22', $tz),
-                new DateTimeImmutable('2011-03-28', $tz),
-                new DateTimeImmutable('2011-05-02', $tz),
+                new \DateTimeImmutable('2011-01-03', $tz),
+                new \DateTimeImmutable('2011-01-05', $tz),
+                new \DateTimeImmutable('2011-01-10', $tz),
+                new \DateTimeImmutable('2011-01-17', $tz),
+                new \DateTimeImmutable('2011-01-18', $tz),
+                new \DateTimeImmutable('2011-01-20', $tz),
+                new \DateTimeImmutable('2011-01-24', $tz),
+                new \DateTimeImmutable('2011-01-31', $tz),
+                new \DateTimeImmutable('2011-03-02', $tz),
+                new \DateTimeImmutable('2011-03-07', $tz),
+                new \DateTimeImmutable('2011-03-14', $tz),
+                new \DateTimeImmutable('2011-03-17', $tz),
+                new \DateTimeImmutable('2011-03-21', $tz),
+                new \DateTimeImmutable('2011-03-22', $tz),
+                new \DateTimeImmutable('2011-03-28', $tz),
+                new \DateTimeImmutable('2011-05-02', $tz),
             ],
             $result
         );
@@ -770,7 +813,7 @@ public function testMonthlyByDay()
     /**
      * @depends testValues
      */
-    public function testMonthlyByDayByMonthDay()
+    public function testMonthlyByDayByMonthDay(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -778,7 +821,7 @@ public function testMonthlyByDayByMonthDay()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=MONTHLY;COUNT=10;BYDAY=MO;BYMONTHDAY=1';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-08-01', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-08-01', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -797,20 +840,20 @@ public function testMonthlyByDayByMonthDay()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-08-01', $tz),
-                new DateTimeImmutable('2012-10-01', $tz),
-                new DateTimeImmutable('2013-04-01', $tz),
-                new DateTimeImmutable('2013-07-01', $tz),
-                new DateTimeImmutable('2014-09-01', $tz),
-                new DateTimeImmutable('2014-12-01', $tz),
-                new DateTimeImmutable('2015-06-01', $tz),
-                new DateTimeImmutable('2016-02-01', $tz),
-                new DateTimeImmutable('2016-08-01', $tz),
-                new DateTimeImmutable('2017-05-01', $tz),
+                new \DateTimeImmutable('2011-08-01', $tz),
+                new \DateTimeImmutable('2012-10-01', $tz),
+                new \DateTimeImmutable('2013-04-01', $tz),
+                new \DateTimeImmutable('2013-07-01', $tz),
+                new \DateTimeImmutable('2014-09-01', $tz),
+                new \DateTimeImmutable('2014-12-01', $tz),
+                new \DateTimeImmutable('2015-06-01', $tz),
+                new \DateTimeImmutable('2016-02-01', $tz),
+                new \DateTimeImmutable('2016-08-01', $tz),
+                new \DateTimeImmutable('2017-05-01', $tz),
             ],
             $result
         );
@@ -819,7 +862,7 @@ public function testMonthlyByDayByMonthDay()
     /**
      * @depends testValues
      */
-    public function testMonthlyByDayBySetPos()
+    public function testMonthlyByDayBySetPos(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -827,7 +870,7 @@ public function testMonthlyByDayBySetPos()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=MONTHLY;COUNT=10;BYDAY=MO,TU,WE,TH,FR;BYSETPOS=1,-1';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-01-03', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-01-03', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -846,20 +889,20 @@ public function testMonthlyByDayBySetPos()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-01-03', $tz),
-                new DateTimeImmutable('2011-01-31', $tz),
-                new DateTimeImmutable('2011-02-01', $tz),
-                new DateTimeImmutable('2011-02-28', $tz),
-                new DateTimeImmutable('2011-03-01', $tz),
-                new DateTimeImmutable('2011-03-31', $tz),
-                new DateTimeImmutable('2011-04-01', $tz),
-                new DateTimeImmutable('2011-04-29', $tz),
-                new DateTimeImmutable('2011-05-02', $tz),
-                new DateTimeImmutable('2011-05-31', $tz),
+                new \DateTimeImmutable('2011-01-03', $tz),
+                new \DateTimeImmutable('2011-01-31', $tz),
+                new \DateTimeImmutable('2011-02-01', $tz),
+                new \DateTimeImmutable('2011-02-28', $tz),
+                new \DateTimeImmutable('2011-03-01', $tz),
+                new \DateTimeImmutable('2011-03-31', $tz),
+                new \DateTimeImmutable('2011-04-01', $tz),
+                new \DateTimeImmutable('2011-04-29', $tz),
+                new \DateTimeImmutable('2011-05-02', $tz),
+                new \DateTimeImmutable('2011-05-31', $tz),
             ],
             $result
         );
@@ -867,16 +910,21 @@ public function testMonthlyByDayBySetPos()
 
     /**
      * @depends testValues
+     *
+     * @throws InvalidDataException
+     * @throws \Exception
      */
-    public function testYearly()
+    public function testYearly(): void
     {
         $vcal = new VCalendar();
+        /** @var VEvent $ev */
         $ev = $vcal->createComponent('VEVENT');
 
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=YEARLY;COUNT=10;INTERVAL=3';
+        /** @var DateTime $dtStart */
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-01-01', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-01-01', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -895,20 +943,20 @@ public function testYearly()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-01-01', $tz),
-                new DateTimeImmutable('2014-01-01', $tz),
-                new DateTimeImmutable('2017-01-01', $tz),
-                new DateTimeImmutable('2020-01-01', $tz),
-                new DateTimeImmutable('2023-01-01', $tz),
-                new DateTimeImmutable('2026-01-01', $tz),
-                new DateTimeImmutable('2029-01-01', $tz),
-                new DateTimeImmutable('2032-01-01', $tz),
-                new DateTimeImmutable('2035-01-01', $tz),
-                new DateTimeImmutable('2038-01-01', $tz),
+                new \DateTimeImmutable('2011-01-01', $tz),
+                new \DateTimeImmutable('2014-01-01', $tz),
+                new \DateTimeImmutable('2017-01-01', $tz),
+                new \DateTimeImmutable('2020-01-01', $tz),
+                new \DateTimeImmutable('2023-01-01', $tz),
+                new \DateTimeImmutable('2026-01-01', $tz),
+                new \DateTimeImmutable('2029-01-01', $tz),
+                new \DateTimeImmutable('2032-01-01', $tz),
+                new \DateTimeImmutable('2035-01-01', $tz),
+                new \DateTimeImmutable('2038-01-01', $tz),
             ],
             $result
         );
@@ -917,7 +965,7 @@ public function testYearly()
     /**
      * @depends testValues
      */
-    public function testYearlyLeapYear()
+    public function testYearlyLeapYear(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -925,7 +973,7 @@ public function testYearlyLeapYear()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=YEARLY;COUNT=3';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2012-02-29', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2012-02-29', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -944,13 +992,13 @@ public function testYearlyLeapYear()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2012-02-29', $tz),
-                new DateTimeImmutable('2016-02-29', $tz),
-                new DateTimeImmutable('2020-02-29', $tz),
+                new \DateTimeImmutable('2012-02-29', $tz),
+                new \DateTimeImmutable('2016-02-29', $tz),
+                new \DateTimeImmutable('2020-02-29', $tz),
             ],
             $result
         );
@@ -959,7 +1007,7 @@ public function testYearlyLeapYear()
     /**
      * @depends testValues
      */
-    public function testYearlyByMonth()
+    public function testYearlyByMonth(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -967,7 +1015,7 @@ public function testYearlyByMonth()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=YEARLY;COUNT=8;INTERVAL=4;BYMONTH=4,10';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-04-07', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-04-07', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -986,18 +1034,18 @@ public function testYearlyByMonth()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-04-07', $tz),
-                new DateTimeImmutable('2011-10-07', $tz),
-                new DateTimeImmutable('2015-04-07', $tz),
-                new DateTimeImmutable('2015-10-07', $tz),
-                new DateTimeImmutable('2019-04-07', $tz),
-                new DateTimeImmutable('2019-10-07', $tz),
-                new DateTimeImmutable('2023-04-07', $tz),
-                new DateTimeImmutable('2023-10-07', $tz),
+                new \DateTimeImmutable('2011-04-07', $tz),
+                new \DateTimeImmutable('2011-10-07', $tz),
+                new \DateTimeImmutable('2015-04-07', $tz),
+                new \DateTimeImmutable('2015-10-07', $tz),
+                new \DateTimeImmutable('2019-04-07', $tz),
+                new \DateTimeImmutable('2019-10-07', $tz),
+                new \DateTimeImmutable('2023-04-07', $tz),
+                new \DateTimeImmutable('2023-10-07', $tz),
             ],
             $result
         );
@@ -1006,7 +1054,7 @@ public function testYearlyByMonth()
     /**
      * @depends testValues
      */
-    public function testYearlyByMonthByDay()
+    public function testYearlyByMonthByDay(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -1014,7 +1062,7 @@ public function testYearlyByMonthByDay()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=YEARLY;COUNT=8;INTERVAL=5;BYMONTH=4,10;BYDAY=1MO,-1SU';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-04-04', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-04-04', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -1033,18 +1081,18 @@ public function testYearlyByMonthByDay()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-04-04', $tz),
-                new DateTimeImmutable('2011-04-24', $tz),
-                new DateTimeImmutable('2011-10-03', $tz),
-                new DateTimeImmutable('2011-10-30', $tz),
-                new DateTimeImmutable('2016-04-04', $tz),
-                new DateTimeImmutable('2016-04-24', $tz),
-                new DateTimeImmutable('2016-10-03', $tz),
-                new DateTimeImmutable('2016-10-30', $tz),
+                new \DateTimeImmutable('2011-04-04', $tz),
+                new \DateTimeImmutable('2011-04-24', $tz),
+                new \DateTimeImmutable('2011-10-03', $tz),
+                new \DateTimeImmutable('2011-10-30', $tz),
+                new \DateTimeImmutable('2016-04-04', $tz),
+                new \DateTimeImmutable('2016-04-24', $tz),
+                new \DateTimeImmutable('2016-10-03', $tz),
+                new \DateTimeImmutable('2016-10-30', $tz),
             ],
             $result
         );
@@ -1053,7 +1101,7 @@ public function testYearlyByMonthByDay()
     /**
      * @depends testValues
      */
-    public function testFastForward()
+    public function testFastForward(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -1061,7 +1109,7 @@ public function testFastForward()
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=YEARLY;COUNT=8;INTERVAL=5;BYMONTH=4,10;BYDAY=1MO,-1SU';
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-04-04', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-04-04', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -1071,7 +1119,7 @@ public function testFastForward()
 
         // The idea is that we're fast-forwarding too far in the future, so
         // there will be no results left.
-        $it->fastForward(new DateTimeImmutable('2020-05-05', new DateTimeZone('UTC')));
+        $it->fastForward(new \DateTimeImmutable('2020-05-05', new \DateTimeZone('UTC')));
 
         $max = 20;
         $result = [];
@@ -1085,13 +1133,13 @@ public function testFastForward()
             $it->next();
         }
 
-        $this->assertEquals([], $result);
+        self::assertEquals([], $result);
     }
 
     /**
      * @depends testValues
      */
-    public function testFastForwardAllDayEventThatStopAtTheStartTime()
+    public function testFastForwardAllDayEventThatStopAtTheStartTime(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
@@ -1100,41 +1148,50 @@ public function testFastForwardAllDayEventThatStopAtTheStartTime()
         $ev->RRULE = 'FREQ=DAILY';
 
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-04-04', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-04-04', new \DateTimeZone('UTC')));
         $ev->add($dtStart);
 
         $dtEnd = $vcal->createProperty('DTSTART');
-        $dtEnd->setDateTime(new DateTimeImmutable('2011-04-05', new DateTimeZone('UTC')));
+        $dtEnd->setDateTime(new \DateTimeImmutable('2011-04-05', new \DateTimeZone('UTC')));
         $ev->add($dtEnd);
 
         $vcal->add($ev);
 
         $it = new EventIterator($vcal, (string) $ev->UID);
 
-        $it->fastForward(new DateTimeImmutable('2011-04-05T000000', new DateTimeZone('UTC')));
+        $it->fastForward(new \DateTimeImmutable('2011-04-05T000000', new \DateTimeZone('UTC')));
 
-        $this->assertEquals(new DateTimeImmutable('2011-04-06'), $it->getDTStart());
+        self::assertEquals(new \DateTimeImmutable('2011-04-06'), $it->getDTStart());
     }
 
     /**
      * @depends testValues
+     *
+     * @throws InvalidDataException
+     * @throws MaxInstancesExceededException
+     * @throws NoInstancesException
+     * @throws \Exception
      */
-    public function testComplexExclusions()
+    public function testComplexExclusions(): void
     {
         $vcal = new VCalendar();
+        /** @var VEvent $ev */
         $ev = $vcal->createComponent('VEVENT');
 
         $ev->UID = 'bla';
         $ev->RRULE = 'FREQ=YEARLY;COUNT=10';
+        /** @var DateTime $dtStart */
         $dtStart = $vcal->createProperty('DTSTART');
 
-        $tz = new DateTimeZone('Canada/Eastern');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-01-01 13:50:20', $tz));
+        $tz = new \DateTimeZone('Canada/Eastern');
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-01-01 13:50:20', $tz));
 
+        /** @var DateTime $exDate1 */
         $exDate1 = $vcal->createProperty('EXDATE');
-        $exDate1->setDateTimes([new DateTimeImmutable('2012-01-01 13:50:20', $tz), new DateTimeImmutable('2014-01-01 13:50:20', $tz)]);
+        $exDate1->setDateTimes([new \DateTimeImmutable('2012-01-01 13:50:20', $tz), new \DateTimeImmutable('2014-01-01 13:50:20', $tz)]);
+        /** @var DateTime $exDate2 */
         $exDate2 = $vcal->createProperty('EXDATE');
-        $exDate2->setDateTimes([new DateTimeImmutable('2016-01-01 13:50:20', $tz)]);
+        $exDate2->setDateTimes([new \DateTimeImmutable('2016-01-01 13:50:20', $tz)]);
 
         $ev->add($dtStart);
         $ev->add($exDate1);
@@ -1155,15 +1212,15 @@ public function testComplexExclusions()
             }
         }
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-01-01 13:50:20', $tz),
-                new DateTimeImmutable('2013-01-01 13:50:20', $tz),
-                new DateTimeImmutable('2015-01-01 13:50:20', $tz),
-                new DateTimeImmutable('2017-01-01 13:50:20', $tz),
-                new DateTimeImmutable('2018-01-01 13:50:20', $tz),
-                new DateTimeImmutable('2019-01-01 13:50:20', $tz),
-                new DateTimeImmutable('2020-01-01 13:50:20', $tz),
+                new \DateTimeImmutable('2011-01-01 13:50:20', $tz),
+                new \DateTimeImmutable('2013-01-01 13:50:20', $tz),
+                new \DateTimeImmutable('2015-01-01 13:50:20', $tz),
+                new \DateTimeImmutable('2017-01-01 13:50:20', $tz),
+                new \DateTimeImmutable('2018-01-01 13:50:20', $tz),
+                new \DateTimeImmutable('2019-01-01 13:50:20', $tz),
+                new \DateTimeImmutable('2020-01-01 13:50:20', $tz),
             ],
             $result
         );
@@ -1172,7 +1229,7 @@ public function testComplexExclusions()
     /**
      * @depends testValues
      */
-    public function testOverriddenEvent()
+    public function testOverriddenEvent(): void
     {
         $vcal = new VCalendar();
 
@@ -1212,21 +1269,21 @@ public function testOverriddenEvent()
             $it->next();
         }
 
-        $tz = new DateTimeZone('UTC');
-        $this->assertEquals([
-            new DateTimeImmutable('2012-01-07 12:00:00', $tz),
-            new DateTimeImmutable('2012-01-08 12:00:00', $tz),
-            new DateTimeImmutable('2012-01-09 12:00:00', $tz),
-            new DateTimeImmutable('2012-01-10 14:00:00', $tz),
-            new DateTimeImmutable('2012-01-11 12:00:00', $tz),
-            new DateTimeImmutable('2012-01-12 12:00:00', $tz),
-            new DateTimeImmutable('2012-01-14 12:00:00', $tz),
-            new DateTimeImmutable('2012-01-15 12:00:00', $tz),
-            new DateTimeImmutable('2012-01-15 14:00:00', $tz),
-            new DateTimeImmutable('2012-01-16 12:00:00', $tz),
+        $tz = new \DateTimeZone('UTC');
+        self::assertEquals([
+            new \DateTimeImmutable('2012-01-07 12:00:00', $tz),
+            new \DateTimeImmutable('2012-01-08 12:00:00', $tz),
+            new \DateTimeImmutable('2012-01-09 12:00:00', $tz),
+            new \DateTimeImmutable('2012-01-10 14:00:00', $tz),
+            new \DateTimeImmutable('2012-01-11 12:00:00', $tz),
+            new \DateTimeImmutable('2012-01-12 12:00:00', $tz),
+            new \DateTimeImmutable('2012-01-14 12:00:00', $tz),
+            new \DateTimeImmutable('2012-01-15 12:00:00', $tz),
+            new \DateTimeImmutable('2012-01-15 14:00:00', $tz),
+            new \DateTimeImmutable('2012-01-16 12:00:00', $tz),
         ], $dates);
 
-        $this->assertEquals([
+        self::assertEquals([
             'baseEvent',
             'baseEvent',
             'baseEvent',
@@ -1243,7 +1300,7 @@ public function testOverriddenEvent()
     /**
      * @depends testValues
      */
-    public function testOverriddenEvent2()
+    public function testOverriddenEvent2(): void
     {
         $vcal = new VCalendar();
 
@@ -1274,14 +1331,14 @@ public function testOverriddenEvent2()
             $it->next();
         }
 
-        $tz = new DateTimeZone('UTC');
-        $this->assertEquals([
-            new DateTimeImmutable('2012-01-12 12:00:00', $tz),
-            new DateTimeImmutable('2012-01-13 12:00:00', $tz),
-            new DateTimeImmutable('2012-01-26 12:00:00', $tz),
+        $tz = new \DateTimeZone('UTC');
+        self::assertEquals([
+            new \DateTimeImmutable('2012-01-12 12:00:00', $tz),
+            new \DateTimeImmutable('2012-01-13 12:00:00', $tz),
+            new \DateTimeImmutable('2012-01-26 12:00:00', $tz),
         ], $dates);
 
-        $this->assertEquals([
+        self::assertEquals([
             'baseEvent',
             'Override!',
             'baseEvent',
@@ -1291,7 +1348,7 @@ public function testOverriddenEvent2()
     /**
      * @depends testValues
      */
-    public function testOverriddenEventNoValuesExpected()
+    public function testOverriddenEventNoValuesExpected(): void
     {
         $vcal = new VCalendar();
         $ev1 = $vcal->createComponent('VEVENT');
@@ -1320,36 +1377,36 @@ public function testOverriddenEventNoValuesExpected()
         // The reported problem was specifically related to the VCALENDAR
         // expansion. In this particular case, we had to forward to the 28th of
         // january.
-        $it->fastForward(new DateTimeImmutable('2012-01-28 23:00:00'));
+        $it->fastForward(new \DateTimeImmutable('2012-01-28 23:00:00'));
 
         // We stop the loop when it hits the 6th of February. Normally this
         // iterator would hit 24, 25 (overridden from 31) and 7 feb but because
         // we 'filter' from the 28th till the 6th, we should get 0 results.
-        while ($it->valid() && $it->getDTStart() < new DateTimeImmutable('2012-02-06 23:00:00')) {
+        while ($it->valid() && $it->getDTStart() < new \DateTimeImmutable('2012-02-06 23:00:00')) {
             $dates[] = $it->getDTStart();
             $summaries[] = (string) $it->getEventObject()->SUMMARY;
             $it->next();
         }
 
-        $this->assertEquals([], $dates);
-        $this->assertEquals([], $summaries);
+        self::assertEquals([], $dates);
+        self::assertEquals([], $summaries);
     }
 
     /**
      * @depends testValues
      */
-    public function testRDATE()
+    public function testRDATE(): void
     {
         $vcal = new VCalendar();
         $ev = $vcal->createComponent('VEVENT');
 
         $ev->UID = 'bla';
         $ev->RDATE = [
-            new DateTimeImmutable('2014-08-07', new DateTimeZone('UTC')),
-            new DateTimeImmutable('2014-08-08', new DateTimeZone('UTC')),
+            new \DateTimeImmutable('2014-08-07', new \DateTimeZone('UTC')),
+            new \DateTimeImmutable('2014-08-08', new \DateTimeZone('UTC')),
         ];
         $dtStart = $vcal->createProperty('DTSTART');
-        $dtStart->setDateTime(new DateTimeImmutable('2011-10-07', new DateTimeZone('UTC')));
+        $dtStart->setDateTime(new \DateTimeImmutable('2011-10-07', new \DateTimeZone('UTC')));
 
         $ev->add($dtStart);
 
@@ -1369,13 +1426,13 @@ public function testRDATE()
             }
         }
 
-        $tz = new DateTimeZone('UTC');
+        $tz = new \DateTimeZone('UTC');
 
-        $this->assertEquals(
+        self::assertEquals(
             [
-                new DateTimeImmutable('2011-10-07', $tz),
-                new DateTimeImmutable('2014-08-07', $tz),
-                new DateTimeImmutable('2014-08-08', $tz),
+                new \DateTimeImmutable('2011-10-07', $tz),
+                new \DateTimeImmutable('2014-08-07', $tz),
+                new \DateTimeImmutable('2014-08-08', $tz),
             ],
             $result
         );
@@ -1384,7 +1441,7 @@ public function testRDATE()
     /**
      * @depends testValues
      */
-    public function testNoMasterBadUID()
+    public function testNoMasterBadUID(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $vcal = new VCalendar();
@@ -1406,6 +1463,6 @@ public function testNoMasterBadUID()
 
         $vcal->add($ev3);
 
-        $it = new EventIterator($vcal, 'broken');
+        new EventIterator($vcal, 'broken');
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/MaxInstancesTest.php b/tests/VObject/Recur/EventIterator/MaxInstancesTest.php
index 6314b3b5a..19dca97af 100644
--- a/tests/VObject/Recur/EventIterator/MaxInstancesTest.php
+++ b/tests/VObject/Recur/EventIterator/MaxInstancesTest.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Recur\EventIterator;
 
-use DateTime;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Reader;
 use Sabre\VObject\Recur\MaxInstancesExceededException;
@@ -10,7 +9,7 @@
 
 class MaxInstancesTest extends TestCase
 {
-    public function testExceedMaxRecurrences()
+    public function testExceedMaxRecurrences(): void
     {
         $this->expectException(MaxInstancesExceededException::class);
         $input = <<<ICS
@@ -29,7 +28,7 @@ public function testExceedMaxRecurrences()
         Settings::$maxRecurrences = 4;
         try {
             $vcal = Reader::read($input);
-            $vcal->expand(new DateTime('2014-08-01'), new DateTime('2014-09-01'));
+            $vcal->expand(new \DateTime('2014-08-01'), new \DateTime('2014-09-01'));
         } finally {
             Settings::$maxRecurrences = $temp;
         }
diff --git a/tests/VObject/Recur/EventIterator/MissingOverriddenTest.php b/tests/VObject/Recur/EventIterator/MissingOverriddenTest.php
index 69af8a8a1..2b1656ecc 100644
--- a/tests/VObject/Recur/EventIterator/MissingOverriddenTest.php
+++ b/tests/VObject/Recur/EventIterator/MissingOverriddenTest.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Recur\EventIterator;
 
-use DateTime;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Reader;
@@ -11,7 +10,7 @@ class MissingOverriddenTest extends TestCase
 {
     use \Sabre\VObject\PHPUnitAssertions;
 
-    public function testExpand()
+    public function testExpand(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -34,9 +33,9 @@ public function testExpand()
 ICS;
 
         $vcal = Reader::read($input);
-        $this->assertInstanceOf(VCalendar::class, $vcal);
+        self::assertInstanceOf(VCalendar::class, $vcal);
 
-        $vcal = $vcal->expand(new DateTime('2011-01-01'), new DateTime('2015-01-01'));
+        $vcal = $vcal->expand(new \DateTime('2011-01-01'), new \DateTime('2015-01-01'));
 
         $output = <<<ICS
 BEGIN:VCALENDAR
@@ -57,6 +56,6 @@ public function testExpand()
 END:VEVENT
 END:VCALENDAR
 ICS;
-        $this->assertVObjectEqualsVObject($output, $vcal);
+        self::assertVObjectEqualsVObject($output, $vcal);
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/NoInstancesTest.php b/tests/VObject/Recur/EventIterator/NoInstancesTest.php
index d89afd197..1eff5f94e 100644
--- a/tests/VObject/Recur/EventIterator/NoInstancesTest.php
+++ b/tests/VObject/Recur/EventIterator/NoInstancesTest.php
@@ -10,7 +10,7 @@
 
 class NoInstancesTest extends TestCase
 {
-    public function testRecurrence()
+    public function testRecurrence(): void
     {
         $this->expectException(NoInstancesException::class);
         $input = <<<ICS
@@ -32,8 +32,8 @@ public function testRecurrence()
 ICS;
 
         $vcal = Reader::read($input);
-        $this->assertInstanceOf(VCalendar::class, $vcal);
+        self::assertInstanceOf(VCalendar::class, $vcal);
 
-        $it = new EventIterator($vcal, 'foo');
+        new EventIterator($vcal, 'foo');
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/OverrideDurationTest.php b/tests/VObject/Recur/EventIterator/OverrideDurationTest.php
index f25ef13d9..8162a6143 100644
--- a/tests/VObject/Recur/EventIterator/OverrideDurationTest.php
+++ b/tests/VObject/Recur/EventIterator/OverrideDurationTest.php
@@ -10,7 +10,7 @@ class OverrideDurationTest extends TestCase
 {
     use \Sabre\VObject\PHPUnitAssertions;
 
-    public function testOverrideDuration()
+    public function testOverrideDuration(): void
     {
         $ics = <<<ICS
 BEGIN:VCALENDAR
@@ -34,19 +34,19 @@ public function testOverrideDuration()
         $vCalendar = Reader::read($ics);
         $eventIterator = new EventIterator($vCalendar->getComponents());
 
-        $this->assertEquals($eventIterator->current()->format('Y-m-d H:i:s'), '2021-05-17 09:00:00', 'recur event start time');
-        $this->assertEquals($eventIterator->getDtEnd()->format('Y-m-d H:i:s'), '2021-05-17 10:00:00', 'recur event end time');
+        self::assertEquals('2021-05-17 09:00:00', $eventIterator->current()->format('Y-m-d H:i:s'), 'recur event start time');
+        self::assertEquals('2021-05-17 10:00:00', $eventIterator->getDtEnd()->format('Y-m-d H:i:s'), 'recur event end time');
 
         $eventIterator->next();
-        $this->assertEquals($eventIterator->current()->format('Y-m-d H:i:s'), '2021-05-18 09:00:00', 'recur event start time');
-        $this->assertEquals($eventIterator->getDtEnd()->format('Y-m-d H:i:s'), '2021-05-18 10:00:00', 'recur event end time');
+        self::assertEquals('2021-05-18 09:00:00', $eventIterator->current()->format('Y-m-d H:i:s'), 'recur event start time');
+        self::assertEquals('2021-05-18 10:00:00', $eventIterator->getDtEnd()->format('Y-m-d H:i:s'), 'recur event end time');
 
         $eventIterator->next();
-        $this->assertEquals($eventIterator->current()->format('Y-m-d H:i:s'), '2021-05-19 09:00:00', 'overridden event start time');
-        $this->assertEquals($eventIterator->getDtEnd()->format('Y-m-d H:i:s'), '2021-05-19 12:00:00', 'overridden event end time');
+        self::assertEquals('2021-05-19 09:00:00', $eventIterator->current()->format('Y-m-d H:i:s'), 'overridden event start time');
+        self::assertEquals('2021-05-19 12:00:00', $eventIterator->getDtEnd()->format('Y-m-d H:i:s'), 'overridden event end time');
 
         $eventIterator->next();
-        $this->assertEquals($eventIterator->current()->format('Y-m-d H:i:s'), '2021-05-20 09:00:00', 'recur event start time');
-        $this->assertEquals($eventIterator->getDtEnd()->format('Y-m-d H:i:s'), '2021-05-20 10:00:00', 'recur event end time');
+        self::assertEquals('2021-05-20 09:00:00', $eventIterator->current()->format('Y-m-d H:i:s'), 'recur event start time');
+        self::assertEquals('2021-05-20 10:00:00', $eventIterator->getDtEnd()->format('Y-m-d H:i:s'), 'recur event end time');
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/OverrideFirstEventTest.php b/tests/VObject/Recur/EventIterator/OverrideFirstEventTest.php
index 150a13980..15c92f04c 100644
--- a/tests/VObject/Recur/EventIterator/OverrideFirstEventTest.php
+++ b/tests/VObject/Recur/EventIterator/OverrideFirstEventTest.php
@@ -2,7 +2,6 @@
 
 namespace Sabre\VObject\Recur\EventIterator;
 
-use DateTime;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Reader;
 
@@ -10,7 +9,7 @@ class OverrideFirstEventTest extends TestCase
 {
     use \Sabre\VObject\PHPUnitAssertions;
 
-    public function testOverrideFirstEvent()
+    public function testOverrideFirstEvent(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -31,7 +30,7 @@ public function testOverrideFirstEvent()
 ICS;
 
         $vcal = Reader::read($input);
-        $vcal = $vcal->expand(new DateTime('2014-08-01'), new DateTime('2014-09-01'));
+        $vcal = $vcal->expand(new \DateTime('2014-08-01'), new \DateTime('2014-09-01'));
 
         $expected = <<<ICS
 BEGIN:VCALENDAR
@@ -69,13 +68,13 @@ public function testOverrideFirstEvent()
 END:VCALENDAR
 ICS;
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $vcal
         );
     }
 
-    public function testRemoveFirstEvent()
+    public function testRemoveFirstEvent(): void
     {
         $input = <<<ICS
 BEGIN:VCALENDAR
@@ -91,7 +90,7 @@ public function testRemoveFirstEvent()
 ICS;
 
         $vcal = Reader::read($input);
-        $vcal = $vcal->expand(new DateTime('2014-08-01'), new DateTime('2014-08-19'));
+        $vcal = $vcal->expand(new \DateTime('2014-08-01'), new \DateTime('2014-08-19'));
 
         $expected = <<<ICS
 BEGIN:VCALENDAR
@@ -111,7 +110,7 @@ public function testRemoveFirstEvent()
 END:VCALENDAR
 ICS;
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $expected,
             $vcal
         );
diff --git a/tests/VObject/Recur/EventIterator/SameDateForRecurringEventsTest.php b/tests/VObject/Recur/EventIterator/SameDateForRecurringEventsTest.php
index 1cbd9792e..ef3ed9b12 100644
--- a/tests/VObject/Recur/EventIterator/SameDateForRecurringEventsTest.php
+++ b/tests/VObject/Recur/EventIterator/SameDateForRecurringEventsTest.php
@@ -16,7 +16,7 @@ class SameDateForRecurringEventsTest extends TestCase
     /**
      * Checking is all events iterated by EventIterator.
      */
-    public function testAllEventsArePresentInIterator()
+    public function testAllEventsArePresentInIterator(): void
     {
         $ics = <<<ICS
 BEGIN:VCALENDAR
@@ -51,6 +51,6 @@ public function testAllEventsArePresentInIterator()
         $vCalendar = Reader::read($ics);
         $eventIterator = new EventIterator($vCalendar->getComponents());
 
-        $this->assertEquals(4, iterator_count($eventIterator), 'in ICS 4 events');
+        self::assertEquals(4, iterator_count($eventIterator), 'in ICS 4 events');
     }
 }
diff --git a/tests/VObject/Recur/FastForwardBeforeTest.php b/tests/VObject/Recur/FastForwardBeforeTest.php
index 3461bd6a5..0426cc5ec 100644
--- a/tests/VObject/Recur/FastForwardBeforeTest.php
+++ b/tests/VObject/Recur/FastForwardBeforeTest.php
@@ -2,13 +2,11 @@
 
 namespace Sabre\VObject\Recur;
 
-use DateTime;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 
 class FastForwardBeforeTest extends TestCase
 {
-    const FF_TIMEOUT = 1000000; // in usec
+    public const FF_TIMEOUT = 1000000; // in usec
 
     private function fastForward(RRuleIterator $ruleIterator, \DateTimeInterface $ffDate)
     {
@@ -22,16 +20,16 @@ private function fastForward(RRuleIterator $ruleIterator, \DateTimeInterface $ff
 
     public function testFastForwardBeforeYearlyBasic()
     {
-        $startDate = new DateTime('1970-10-23 00:00:00', new DateTimeZone('zulu'));
-        $ffDate = new DateTime('midnight', new DateTimeZone('zulu'));
+        $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(99999, 1, 1);
         $rrule = new RRuleIterator('FREQ=YEARLY', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
         $year = 60 * 60 * 24 * 365;
-        $expected = (new DateTime())
-            ->setTimezone(new DateTimeZone('zulu'))
+        $expected = (new \DateTime())
+            ->setTimezone(new \DateTimeZone('zulu'))
             ->setDate(99998, 10, 23)
             ->setTime(0, 0, 0)
             ->getTimestamp();
@@ -86,7 +84,7 @@ public function testFastForwardBeforeYearlyBasic()
     public function testFastForwardBeforeYearlyByYearDay()
     {
         $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone('zulu'));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(99999, 1, 5);
         $rrule = new RRuleIterator('FREQ=YEARLY;BYYEARDAY=1,20,300', $startDate);
 
@@ -94,8 +92,8 @@ public function testFastForwardBeforeYearlyByYearDay()
 
         // 1st day
         $day = 60 * 60 * 24;
-        $expected = (new DateTime())
-            ->setTimezone(new DateTimeZone('zulu'))
+        $expected = (new \DateTime())
+            ->setTimezone(new \DateTimeZone('zulu'))
             ->setDate(99999, 1, 1)
             ->setTime(0, 0, 0)
             ->getTimestamp();
@@ -140,7 +138,7 @@ public function testFastForwardBeforeYearlyByYearDay()
     public function testFastForwardBeforeYearlyByWeekNo()
     {
         $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone('zulu'));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(99999, 1, 5);
         $rrule = new RRuleIterator('FREQ=YEARLY;BYWEEKNO=1,20', $startDate);
 
@@ -150,8 +148,8 @@ public function testFastForwardBeforeYearlyByWeekNo()
         $week = 7 * $day;
 
         // 1st week
-        $expected = (new DateTime())
-            ->setTimezone(new DateTimeZone('zulu'))
+        $expected = (new \DateTime())
+            ->setTimezone(new \DateTimeZone('zulu'))
             ->setDate(99999, 1, 4)
             ->setTime(0, 0, 0)
             ->getTimestamp();
@@ -166,13 +164,13 @@ public function testFastForwardBeforeYearlyByWeekNo()
     public function testFastForwardBeforeYearlyAdvanced()
     {
         $startDate = new \DateTime('1970-10-23 12:34:56', new \DateTimeZone('zulu'));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(10000, 1, 2)->setTime(8, 44, 13);
         $rrule = new RRuleIterator('FREQ=YEARLY;INTERVAL=2;BYMONTH=1;BYDAY=SU;BYHOUR=8,9;BYMINUTE=30', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('zulu')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('zulu')))
             ->setDate(10000, 1, 2)
             ->setTime(8, 30, 56)
             ->getTimestamp();
@@ -216,7 +214,7 @@ public function testFastForwardBeforeYearlyAdvanced()
 
         // jump to 6th january 10002
         $rrule->next();
-        $expected = (new DateTime('midnight', new DateTimeZone('zulu')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('zulu')))
             ->setDate(10002, 1, 6)
             ->setTime(8, 30, 56)
             ->getTimestamp();
@@ -230,13 +228,13 @@ public function testFastForwardBeforeYearlyAdvanced()
     public function testFastForwardBeforeMonthlyBasic()
     {
         $startDate = new \DateTime('1970-10-23 22:42:31', new \DateTimeZone('zulu'));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(18000, 1, 30);
         $rrule = new RRuleIterator('FREQ=MONTHLY', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('zulu')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('zulu')))
             ->setDate(18000, 1, 23)
             ->setTime(22, 42, 31)
             ->getTimestamp();
@@ -276,55 +274,55 @@ public function testFastForwardBeforeMonthly31thDay()
     {
         $timezone = 'America/New_York';
         $startDate = new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(18000, 2, 1);
         $rrule = new RRuleIterator('FREQ=MONTHLY', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new \DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(18000, 1, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // march
         $rrule->next();
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(18000, 3, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // may
         $rrule->next();
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(18000, 5, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // july
         $rrule->next();
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(18000, 7, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // august
         $rrule->next();
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(18000, 8, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // october
         $rrule->next();
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(18000, 10, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // december
         $rrule->next();
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(18000, 12, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
@@ -333,8 +331,8 @@ public function testFastForwardBeforeMonthly31thDay()
     public function testFastForwardBeforeMonthlyAdvanced()
     {
         $timezone = 'America/New_York';
-        $startDate = new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $startDate = new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(8000, 1, 6);
         // every 2 months on the 1st Monday, 2nd Tuesday, 3rd Wednesday and 4th Thursday
         $rrule = new RRuleIterator('FREQ=MONTHLY;INTERVAL=2;BYDAY=1MO,2TU,3WE,4TH', $startDate);
@@ -342,48 +340,48 @@ public function testFastForwardBeforeMonthlyAdvanced()
         $this->fastForward($rrule, $ffDate);
 
         // monday
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(8000, 1, 3)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // tuesday
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(8000, 1, 11)
             ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // wednesday
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(8000, 1, 19)
             ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // thursday
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(8000, 1, 27)
             ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // monday march
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(8000, 3, 6)
             ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // tuesday
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(8000, 3, 14)
             ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // wednesday (this month starts on wednesday so that's just the next day)
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(8000, 3, 15)
             ->getTimestamp();
         $rrule->next();
@@ -391,7 +389,7 @@ public function testFastForwardBeforeMonthlyAdvanced()
 
         // thursday
         $expected += 8 * 24 * 60 * 60;
-        $expected = (new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone)))
             ->setDate(8000, 3, 23)
             ->getTimestamp();
         $rrule->next();
@@ -402,13 +400,13 @@ public function testFastForwardBeforeDailyBasic()
     {
         $timezone = 'America/New_York';
         $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone($timezone));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(4000, 1, 2);
         $rrule = new RRuleIterator('FREQ=DAILY', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(4000, 1, 1)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
@@ -442,14 +440,14 @@ public function testFastForwardBeforeDailyAdvanced()
     {
         $timezone = 'America/New_York';
         $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone($timezone));
-        $ffDate = new \DateTime('midnight', new DateTimeZone($timezone));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone($timezone));
         $ffDate->setDate(4000, 1, 4)->setTime(16, 30, 0);
         // every 10 days at 16, 17 and 18
         $rrule = new RRuleIterator('FREQ=DAILY;BYHOUR=16,17,18;INTERVAL=10', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(4000, 1, 4)
             ->setTime(16, 0, 0)
             ->getTimestamp();
@@ -490,13 +488,13 @@ public function testFastForwardBeforeHourlyBasic()
     {
         $timezone = 'America/New_York';
         $startDate = new \DateTime('1970-10-23 00:12:34', new \DateTimeZone($timezone));
-        $ffDate = new \DateTime('midnight', new DateTimeZone($timezone));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone($timezone));
         $ffDate->setDate(4000, 1, 2)->setTime(2, 0, 0);
         $rrule = new RRuleIterator('FREQ=HOURLY', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(4000, 1, 2)
             ->setTime(1, 12, 34)
             ->getTimestamp();
@@ -531,21 +529,21 @@ public function testFastForwardBeforeNotInFrequency()
     {
         $timezone = 'America/New_York';
         $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone($timezone));
-        $ffDate = new \DateTime('midnight', new DateTimeZone($timezone));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone($timezone));
         $ffDate->setDate(2023, 3, 15)->setTime(1, 0, 0);
         // every leap years
         $rrule = new RRuleIterator('FREQ=YEARLY;BYMONTH=2;BYMONTHDAY=29', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(2020, 2, 29)
             ->setTime(0, 0, 0)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // the next leap year
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(2024, 2, 29)
             ->setTime(0, 0, 0)
             ->getTimestamp();
@@ -555,10 +553,10 @@ public function testFastForwardBeforeNotInFrequency()
 
     public function testFastForwardBeforeMultipleTimesBasic()
     {
-        $startDate = new DateTime('2020-01-02 00:00:00', new DateTimeZone('zulu'));
-        $ffDate = new DateTime('2020-01-18 00:00:00', new DateTimeZone('zulu'));
+        $startDate = new \DateTime('2020-01-02 00:00:00', new \DateTimeZone('zulu'));
+        $ffDate = new \DateTime('2020-01-18 00:00:00', new \DateTimeZone('zulu'));
         $rrule = new RRuleIterator('FREQ=WEEKLY', $startDate);
-        $expected = new DateTime('2020-01-16 00:00:00', new DateTimeZone('zulu'));
+        $expected = new \DateTime('2020-01-16 00:00:00', new \DateTimeZone('zulu'));
 
         $this->fastForward($rrule, $ffDate);
         $this->assertEquals($expected->getTimestamp(), $rrule->current()->getTimestamp());
diff --git a/tests/VObject/Recur/FastForwardTest.php b/tests/VObject/Recur/FastForwardTest.php
index 7a305b4ad..62effc4de 100644
--- a/tests/VObject/Recur/FastForwardTest.php
+++ b/tests/VObject/Recur/FastForwardTest.php
@@ -2,13 +2,11 @@
 
 namespace Sabre\VObject\Recur;
 
-use DateTime;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 
 class FastForwardTest extends TestCase
 {
-    const FF_TIMEOUT = 1000000; // in usec
+    public const FF_TIMEOUT = 1000000; // in usec
 
     private function fastForward(RRuleIterator $ruleIterator, \DateTimeInterface $ffDate)
     {
@@ -22,16 +20,16 @@ private function fastForward(RRuleIterator $ruleIterator, \DateTimeInterface $ff
 
     public function testFastForwardYearlyBasic()
     {
-        $startDate = new DateTime('1970-10-23 00:00:00', new DateTimeZone('zulu'));
-        $ffDate = new DateTime('midnight', new DateTimeZone('zulu'));
+        $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(99999, 1, 1);
         $rrule = new RRuleIterator('FREQ=YEARLY', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
         $year = 60 * 60 * 24 * 365;
-        $expected = (new DateTime())
-            ->setTimezone(new DateTimeZone('zulu'))
+        $expected = (new \DateTime())
+            ->setTimezone(new \DateTimeZone('zulu'))
             ->setDate(99999, 10, 23)
             ->setTime(0, 0, 0)
             ->getTimestamp();
@@ -72,15 +70,15 @@ public function testFastForwardYearlyBasic()
     public function testFastForwardYearlyByYearDay()
     {
         $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone('zulu'));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(99998, 12, 31);
         $rrule = new RRuleIterator('FREQ=YEARLY;BYYEARDAY=1,20,300', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
         $day = 60 * 60 * 24;
-        $expected = (new DateTime())
-            ->setTimezone(new DateTimeZone('zulu'))
+        $expected = (new \DateTime())
+            ->setTimezone(new \DateTimeZone('zulu'))
             ->setDate(99999, 1, 1)// 20th day
             ->setTime(0, 0, 0)
             ->getTimestamp();
@@ -116,7 +114,7 @@ public function testFastForwardYearlyByYearDay()
     public function testFastForwardYearlyByWeekNo()
     {
         $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone('zulu'));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(99999, 1, 1);
         $rrule = new RRuleIterator('FREQ=YEARLY;BYWEEKNO=1,20', $startDate);
 
@@ -124,8 +122,8 @@ public function testFastForwardYearlyByWeekNo()
 
         $day = 60 * 60 * 24;
         $week = 7 * $day;
-        $expected = (new DateTime())
-            ->setTimezone(new DateTimeZone('zulu'))
+        $expected = (new \DateTime())
+            ->setTimezone(new \DateTimeZone('zulu'))
             ->setDate(99999, 1, 4)// 1st day
             ->setTime(0, 0, 0)
             ->getTimestamp();
@@ -138,13 +136,13 @@ public function testFastForwardYearlyByWeekNo()
     public function testFastForwardYearlyAdvanced()
     {
         $startDate = new \DateTime('1970-10-23 12:34:56', new \DateTimeZone('zulu'));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(9999, 1, 20)->setTime(0, 0, 13);
         $rrule = new RRuleIterator('FREQ=YEARLY;INTERVAL=2;BYMONTH=1;BYDAY=SU;BYHOUR=8,9;BYMINUTE=30', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('zulu')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('zulu')))
             ->setDate(10000, 1, 2)
             ->setTime(8, 30, 56)
             ->getTimestamp();
@@ -188,7 +186,7 @@ public function testFastForwardYearlyAdvanced()
 
         // jump to 6th january 10002
         $rrule->next();
-        $expected = (new DateTime('midnight', new DateTimeZone('zulu')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('zulu')))
             ->setDate(10002, 1, 6)
             ->setTime(8, 30, 56)
             ->getTimestamp();
@@ -202,13 +200,13 @@ public function testFastForwardYearlyAdvanced()
     public function testFastForwardMonthlyBasic()
     {
         $startDate = new \DateTime('1970-10-23 22:42:31', new \DateTimeZone('zulu'));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(18000, 1, 1);
         $rrule = new RRuleIterator('FREQ=MONTHLY', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('zulu')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('zulu')))
             ->setDate(18000, 1, 23)
             ->setTime(22, 42, 31)
             ->getTimestamp();
@@ -248,20 +246,20 @@ public function testFastForwardMonthly31thDay()
     {
         $timezone = 'America/New_York';
         $startDate = new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(18000, 1, 1);
         $rrule = new RRuleIterator('FREQ=MONTHLY', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('America/New_York')))
             ->setDate(18000, 1, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // march
         $rrule->next();
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('America/New_York')))
             ->setDate(18000, 3, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
@@ -269,35 +267,35 @@ public function testFastForwardMonthly31thDay()
         // may
         $rrule->next();
         $expected += (30 + 31) * 24 * 60 * 60;
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('America/New_York')))
             ->setDate(18000, 5, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // july
         $rrule->next();
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('America/New_York')))
             ->setDate(18000, 7, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // august
         $rrule->next();
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('America/New_York')))
             ->setDate(18000, 8, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // october
         $rrule->next();
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('America/New_York')))
             ->setDate(18000, 10, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // december
         $rrule->next();
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('America/New_York')))
             ->setDate(18000, 12, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
@@ -306,63 +304,63 @@ public function testFastForwardMonthly31thDay()
     public function testFastForwardMonthlyAdvanced()
     {
         $timezone = 'America/New_York';
-        $startDate = new \DateTime('1970-01-31 00:00:00', new DateTimeZone($timezone));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $startDate = new \DateTime('1970-01-31 00:00:00', new \DateTimeZone($timezone));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(8000, 1, 1);
         $rrule = new RRuleIterator('FREQ=MONTHLY;INTERVAL=2;BYDAY=1MO,2TU,3WE,4TH', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
         // monday
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(8000, 1, 3)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // tuesday
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(8000, 1, 11)
             ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // wednesday
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(8000, 1, 19)
             ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // thursday
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(8000, 1, 27)
             ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // monday march
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(8000, 3, 6)
             ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // tuesday
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(8000, 3, 14)
             ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // wednesday (this month starts on wednesday so that's just the next day)
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(8000, 3, 15)
             ->getTimestamp();
         $rrule->next();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
 
         // thursday
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(8000, 3, 23)
             ->getTimestamp();
         $rrule->next();
@@ -373,13 +371,13 @@ public function testFastForwardDailyBasic()
     {
         $timezone = 'America/New_York';
         $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone($timezone));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(4000, 1, 1);
         $rrule = new RRuleIterator('FREQ=DAILY', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(4000, 1, 1)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
@@ -413,13 +411,13 @@ public function testFastForwardDailyAdvanced()
     {
         $timezone = 'America/New_York';
         $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone($timezone));
-        $ffDate = new \DateTime('midnight', new DateTimeZone('zulu'));
+        $ffDate = new \DateTime('midnight', new \DateTimeZone('zulu'));
         $ffDate->setDate(4000, 1, 1);
         $rrule = new RRuleIterator('FREQ=DAILY;BYHOUR=16,17,18;INTERVAL=10', $startDate);
 
         $this->fastForward($rrule, $ffDate);
 
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(4000, 1, 4)
             ->setTime(16, 0, 0)
             ->getTimestamp();
diff --git a/tests/VObject/Recur/FastForwardToEndTest.php b/tests/VObject/Recur/FastForwardToEndTest.php
index 992f2b9d8..1073a95df 100644
--- a/tests/VObject/Recur/FastForwardToEndTest.php
+++ b/tests/VObject/Recur/FastForwardToEndTest.php
@@ -2,15 +2,13 @@
 
 namespace Sabre\VObject\Recur;
 
-use DateTime;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 
 class FastForwardToEndTest extends TestCase
 {
-    const FF_TIMEOUT = 1000000; // in usec
+    public const FF_TIMEOUT = 1000000; // in usec
 
-    private function fastForwardToEnd(RRuleIterator $ruleIterator, $enfoceTiming = true)
+    private function fastForwardToEnd(RRuleIterator $ruleIterator, $enfoceTiming = true): void
     {
         $ru = getrusage();
         $startTime = $ru['ru_utime.tv_sec'] * 1000000 + $ru['ru_utime.tv_usec'];
@@ -22,47 +20,47 @@ private function fastForwardToEnd(RRuleIterator $ruleIterator, $enfoceTiming = t
         $this->assertNotNull($ruleIterator->current());
     }
 
-    public function testFastForwardToEndWithoutEndYearlyBasic()
+    public function testFastForwardToEndWithoutEndYearlyBasic(): void
     {
-        $startDate = new DateTime('1970-10-23 00:00:00', new DateTimeZone('zulu'));
+        $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone('zulu'));
         $rrule = new RRuleIterator('FREQ=YEARLY', $startDate);
 
         $this->expectException(\LogicException::class);
         $rrule->fastForwardToEnd();
     }
 
-    public function testFastForwardToEndCountYearlyBasic()
+    public function testFastForwardToEndCountYearlyBasic(): void
     {
-        $startDate = new DateTime('1970-10-23 00:00:00', new DateTimeZone('zulu'));
+        $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone('zulu'));
         $rrule = new RRuleIterator('FREQ=YEARLY;COUNT=7777', $startDate);
 
         // We do not enforce the timing in case of a count rule as we cannot optimize it
         $this->fastForwardToEnd($rrule, false);
 
-        $expected = (new DateTime())
-            ->setTimezone(new DateTimeZone('zulu'))
+        $expected = (new \DateTime())
+            ->setTimezone(new \DateTimeZone('zulu'))
             ->setDate(9746, 10, 23)
             ->setTime(0, 0, 0)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
     }
 
-    public function testFastForwardToEndUntilYearlyBasic()
+    public function testFastForwardToEndUntilYearlyBasic(): void
     {
-        $startDate = new DateTime('1970-10-23 00:00:00', new DateTimeZone('zulu'));
+        $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone('zulu'));
         $rrule = new RRuleIterator('FREQ=YEARLY;UNTIL=97461212T000000', $startDate);
 
         $this->fastForwardToEnd($rrule);
 
-        $expected = (new DateTime())
-            ->setTimezone(new DateTimeZone('zulu'))
+        $expected = (new \DateTime())
+            ->setTimezone(new \DateTimeZone('zulu'))
             ->setDate(9746, 10, 23)
             ->setTime(0, 0, 0)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
     }
 
-    public function testFastForwardToEndCountYearlyByYearDay()
+    public function testFastForwardToEndCountYearlyByYearDay(): void
     {
         $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone('zulu'));
         $rrule = new RRuleIterator('FREQ=YEARLY;BYYEARDAY=1,20,300;COUNT=10000', $startDate);
@@ -70,23 +68,23 @@ public function testFastForwardToEndCountYearlyByYearDay()
         // We do not enforce the timing in case of a count rule as we cannot optimize it
         $this->fastForwardToEnd($rrule, false);
 
-        $expected = (new DateTime())
-            ->setTimezone(new DateTimeZone('zulu'))
+        $expected = (new \DateTime())
+            ->setTimezone(new \DateTimeZone('zulu'))
             ->setDate(5303, 1, 20)
             ->setTime(0, 0, 0)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
     }
 
-    public function testFastForwardToEndUntilYearlyByYearDay()
+    public function testFastForwardToEndUntilYearlyByYearDay(): void
     {
         $startDate = new \DateTime('1970-10-23 00:00:00', new \DateTimeZone('zulu'));
         $rrule = new RRuleIterator('FREQ=YEARLY;BYYEARDAY=1,20,300;UNTIL=53030808T000000', $startDate);
 
         $this->fastForwardToEnd($rrule);
 
-        $expected = (new DateTime())
-            ->setTimezone(new DateTimeZone('zulu'))
+        $expected = (new \DateTime())
+            ->setTimezone(new \DateTimeZone('zulu'))
             ->setDate(5303, 1, 20)
             ->setTime(0, 0, 0)
             ->getTimestamp();
@@ -135,7 +133,7 @@ public function testFastForwardToEndCountYearlyAdvanced()
         // We do not enforce the timing in case of a count rule as we cannot optimize it
         $this->fastForwardToEnd($rrule, false);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('zulu')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('zulu')))
             ->setDate(4226, 1, 1)
             ->setTime(8, 30, 56)
             ->getTimestamp();
@@ -149,7 +147,7 @@ public function testFastForwardToEndUntilYearlyAdvanced()
 
         $this->fastForwardToEnd($rrule);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('zulu')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('zulu')))
             ->setDate(4218, 1, 25)
             ->setTime(8, 30, 56)
             ->getTimestamp();
@@ -164,7 +162,7 @@ public function testFastForwardToEndCountMonthlyBasic()
         // We do not enforce the timing in case of a count rule as we cannot optimize it
         $this->fastForwardToEnd($rrule, false);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('zulu')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('zulu')))
             ->setDate(2804, 1, 23)
             ->setTime(22, 42, 31)
             ->getTimestamp();
@@ -178,7 +176,7 @@ public function testFastForwardToEndUntilMonthlyBasic()
 
         $this->fastForwardToEnd($rrule);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('zulu')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('zulu')))
             ->setDate(2803, 12, 23)
             ->setTime(22, 42, 31)
             ->getTimestamp();
@@ -196,7 +194,7 @@ public function testFastForwardToEndCountMonthly31thDay()
         // We do not enforce the timing in case of a count rule as we cannot optimize it
         $this->fastForwardToEnd($rrule, false);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('America/New_York')))
             ->setDate(3398, 10, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
@@ -213,7 +211,7 @@ public function testFastForwardToEndCountMonthly31thDayPHP81()
         // We do not enforce the timing in case of a count rule as we cannot optimize it
         $this->fastForwardToEnd($rrule, false);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('America/New_York')))
             ->setDate(3398, 7, 31);
         $this->assertEquals($expected->getTimestamp(), $rrule->current()->getTimestamp());
     }
@@ -225,7 +223,7 @@ public function testFastForwardToEndUntilMonthly31thDay()
 
         $this->fastForwardToEnd($rrule);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('America/New_York')))
             ->setDate(3398, 8, 31)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
@@ -233,14 +231,14 @@ public function testFastForwardToEndUntilMonthly31thDay()
 
     public function testFastForwardToEndCountMonthlyAdvanced()
     {
-        $startDate = new \DateTime('1970-01-31 00:00:00', new DateTimeZone('America/New_York'));
+        $startDate = new \DateTime('1970-01-31 00:00:00', new \DateTimeZone('America/New_York'));
         // every 2 months on the 1st Monday, 2nd Tuesday, 3rd Wednesday and 4th Thursday
         $rrule = new RRuleIterator('FREQ=MONTHLY;INTERVAL=2;BYDAY=1MO,2TU,3WE,4TH;COUNT=10000', $startDate);
 
         // We do not enforce the timing in case of a count rule as we cannot optimize it
         $this->fastForwardToEnd($rrule, false);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('America/New_York')))
             ->setDate(2386, 9, 17)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
@@ -248,13 +246,13 @@ public function testFastForwardToEndCountMonthlyAdvanced()
 
     public function testFastForwardToEndUntilMonthlyAdvanced()
     {
-        $startDate = new \DateTime('1970-01-31 00:00:00', new DateTimeZone('America/New_York'));
+        $startDate = new \DateTime('1970-01-31 00:00:00', new \DateTimeZone('America/New_York'));
         // every 2 months on the 1st Monday, 2nd Tuesday, 3rd Wednesday and 4th Thursday
         $rrule = new RRuleIterator('FREQ=MONTHLY;INTERVAL=2;BYDAY=1MO,2TU,3WE,4TH;UNTIL=23860914T092500', $startDate);
 
         $this->fastForwardToEnd($rrule);
 
-        $expected = (new DateTime('midnight', new DateTimeZone('America/New_York')))
+        $expected = (new \DateTime('midnight', new \DateTimeZone('America/New_York')))
             ->setDate(2386, 9, 9)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
@@ -269,7 +267,7 @@ public function testFastForwardToEndCountDailyBasic()
         // We do not enforce the timing in case of a count rule as we cannot optimize it
         $this->fastForwardToEnd($rrule, false);
 
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(2244, 8, 6)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
@@ -283,7 +281,7 @@ public function testFastForwardToEndUntilDailyBasic()
 
         $this->fastForwardToEnd($rrule);
 
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(2244, 8, 6)
             ->getTimestamp();
         $this->assertEquals($expected, $rrule->current()->getTimestamp());
@@ -299,7 +297,7 @@ public function testFastForwardToEndCountDailyAdvanced()
         // We do not enforce the timing in case of a count rule as we cannot optimize it
         $this->fastForwardToEnd($rrule, false);
 
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(2062, 1, 13)
             ->setTime(18, 0, 0)
             ->getTimestamp();
@@ -315,7 +313,7 @@ public function testFastForwardToEndUntilDailyAdvanced()
 
         $this->fastForwardToEnd($rrule);
 
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(2062, 1, 13)
             ->setTime(18, 0, 0)
             ->getTimestamp();
@@ -331,7 +329,7 @@ public function testFastForwardToEndCountHourlyBasic()
         // We do not enforce the timing in case of a count rule as we cannot optimize it
         $this->fastForwardToEnd($rrule, false);
 
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(1982, 3, 21)
             ->setTime(2, 12, 34)
             ->getTimestamp();
@@ -346,7 +344,7 @@ public function testFastForwardToEndUntilHourlyBasic()
 
         $this->fastForwardToEnd($rrule);
 
-        $expected = (new DateTime('midnight', new DateTimeZone($timezone)))
+        $expected = (new \DateTime('midnight', new \DateTimeZone($timezone)))
             ->setDate(1982, 3, 21)
             ->setTime(2, 12, 34)
             ->getTimestamp();
diff --git a/tests/VObject/Recur/RDateIteratorTest.php b/tests/VObject/Recur/RDateIteratorTest.php
index 453d8cf73..5dfe57381 100644
--- a/tests/VObject/Recur/RDateIteratorTest.php
+++ b/tests/VObject/Recur/RDateIteratorTest.php
@@ -2,56 +2,54 @@
 
 namespace Sabre\VObject\Recur;
 
-use DateTimeImmutable;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 
 class RDateIteratorTest extends TestCase
 {
-    public function testSimple()
+    public function testSimple(): void
     {
-        $utc = new DateTimeZone('UTC');
-        $it = new RDateIterator('20140901T000000Z,20141001T000000Z', new DateTimeImmutable('2014-08-01 00:00:00', $utc));
+        $utc = new \DateTimeZone('UTC');
+        $it = new RDateIterator('20140901T000000Z,20141001T000000Z', new \DateTimeImmutable('2014-08-01 00:00:00', $utc));
 
         $expected = [
-            new DateTimeImmutable('2014-08-01 00:00:00', $utc),
-            new DateTimeImmutable('2014-09-01 00:00:00', $utc),
-            new DateTimeImmutable('2014-10-01 00:00:00', $utc),
+            new \DateTimeImmutable('2014-08-01 00:00:00', $utc),
+            new \DateTimeImmutable('2014-09-01 00:00:00', $utc),
+            new \DateTimeImmutable('2014-10-01 00:00:00', $utc),
         ];
 
-        $this->assertEquals(
+        self::assertEquals(
             $expected,
             iterator_to_array($it)
         );
 
-        $this->assertFalse($it->isInfinite());
+        self::assertFalse($it->isInfinite());
     }
 
-    public function testTimezone()
+    public function testTimezone(): void
     {
-        $tz = new DateTimeZone('Europe/Berlin');
-        $it = new RDateIterator('20140901T000000,20141001T000000', new DateTimeImmutable('2014-08-01 00:00:00', $tz));
+        $tz = new \DateTimeZone('Europe/Berlin');
+        $it = new RDateIterator('20140901T000000,20141001T000000', new \DateTimeImmutable('2014-08-01 00:00:00', $tz));
 
         $expected = [
-            new DateTimeImmutable('2014-08-01 00:00:00', $tz),
-            new DateTimeImmutable('2014-09-01 00:00:00', $tz),
-            new DateTimeImmutable('2014-10-01 00:00:00', $tz),
+            new \DateTimeImmutable('2014-08-01 00:00:00', $tz),
+            new \DateTimeImmutable('2014-09-01 00:00:00', $tz),
+            new \DateTimeImmutable('2014-10-01 00:00:00', $tz),
         ];
 
-        $this->assertEquals(
+        self::assertEquals(
             $expected,
             iterator_to_array($it)
         );
 
-        $this->assertFalse($it->isInfinite());
+        self::assertFalse($it->isInfinite());
     }
 
-    public function testFastForward()
+    public function testFastForward(): void
     {
-        $utc = new DateTimeZone('UTC');
-        $it = new RDateIterator('20140901T000000Z,20141001T000000Z', new DateTimeImmutable('2014-08-01 00:00:00', $utc));
+        $utc = new \DateTimeZone('UTC');
+        $it = new RDateIterator('20140901T000000Z,20141001T000000Z', new \DateTimeImmutable('2014-08-01 00:00:00', $utc));
 
-        $it->fastForward(new DateTimeImmutable('2014-08-15 00:00:00'));
+        $it->fastForward(new \DateTimeImmutable('2014-08-15 00:00:00'));
 
         $result = [];
         while ($it->valid()) {
@@ -60,15 +58,15 @@ public function testFastForward()
         }
 
         $expected = [
-            new DateTimeImmutable('2014-09-01 00:00:00', $utc),
-            new DateTimeImmutable('2014-10-01 00:00:00', $utc),
+            new \DateTimeImmutable('2014-09-01 00:00:00', $utc),
+            new \DateTimeImmutable('2014-10-01 00:00:00', $utc),
         ];
 
-        $this->assertEquals(
+        self::assertEquals(
             $expected,
             $result
         );
 
-        $this->assertFalse($it->isInfinite());
+        self::assertFalse($it->isInfinite());
     }
 }
diff --git a/tests/VObject/Recur/RRuleIteratorTest.php b/tests/VObject/Recur/RRuleIteratorTest.php
index 6cb3feb5b..3384506f5 100644
--- a/tests/VObject/Recur/RRuleIteratorTest.php
+++ b/tests/VObject/Recur/RRuleIteratorTest.php
@@ -2,15 +2,12 @@
 
 namespace Sabre\VObject\Recur;
 
-use DateTime;
-use DateTimeImmutable;
-use DateTimeZone;
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\InvalidDataException;
 
 class RRuleIteratorTest extends TestCase
 {
-    public function testHourly()
+    public function testHourly(): void
     {
         $this->parse(
             'FREQ=HOURLY;INTERVAL=3;COUNT=12',
@@ -33,7 +30,7 @@ public function testHourly()
         );
     }
 
-    public function testDaily()
+    public function testDaily(): void
     {
         $this->parse(
             'FREQ=DAILY;INTERVAL=3;UNTIL=20111025T000000Z',
@@ -47,11 +44,11 @@ public function testDaily()
                 '2011-10-22 00:00:00',
                 '2011-10-25 00:00:00',
             ],
-            'daily', null, 3, new DateTime('2011-10-25')
+            'daily', null, 3, new \DateTime('2011-10-25')
         );
     }
 
-    public function testDailyByDayByHour()
+    public function testDailyByDayByHour(): void
     {
         $this->parse(
             'FREQ=DAILY;BYDAY=SA,SU;BYHOUR=6,7',
@@ -74,7 +71,7 @@ public function testDailyByDayByHour()
         );
     }
 
-    public function testDailyByHour()
+    public function testDailyByHour(): void
     {
         $this->parse(
             'FREQ=DAILY;INTERVAL=2;BYHOUR=10,11,12,13,14,15',
@@ -97,7 +94,7 @@ public function testDailyByHour()
         );
     }
 
-    public function testDailyByDay()
+    public function testDailyByDay(): void
     {
         $this->parse(
             'FREQ=DAILY;INTERVAL=2;BYDAY=TU,WE,FR',
@@ -120,7 +117,7 @@ public function testDailyByDay()
         );
     }
 
-    public function testDailyCount()
+    public function testDailyCount(): void
     {
         $this->parse(
             'FREQ=DAILY;COUNT=5',
@@ -136,7 +133,7 @@ public function testDailyCount()
         );
     }
 
-    public function testDailyByMonth()
+    public function testDailyByMonth(): void
     {
         $this->parse(
             'FREQ=DAILY;BYMONTH=9,10;BYDAY=SU',
@@ -154,7 +151,24 @@ public function testDailyByMonth()
         );
     }
 
-    public function testWeekly()
+    /**
+     * This test can take some seconds to complete.
+     * The "large" annotation means phpunit will let it run for
+     * up to 60 seconds by default.
+     *
+     * @large
+     */
+    public function testDailyBySetPosLoop(): void
+    {
+        $this->parse(
+            'FREQ=DAILY;INTERVAL=7;BYDAY=MO',
+            '2022-03-15',
+            [],
+            'daily', null, 7, null, '2022-05-01'
+        );
+    }
+
+    public function testWeekly(): void
     {
         $this->parse(
             'FREQ=WEEKLY;INTERVAL=2;COUNT=10',
@@ -175,7 +189,7 @@ public function testWeekly()
         );
     }
 
-    public function testWeeklyByDay()
+    public function testWeeklyByDay(): void
     {
         $this->parse(
             'FREQ=WEEKLY;INTERVAL=1;COUNT=4;BYDAY=MO;WKST=SA',
@@ -190,7 +204,7 @@ public function testWeeklyByDay()
         );
     }
 
-    public function testWeeklyByDay2()
+    public function testWeeklyByDay2(): void
     {
         $this->parse(
             'FREQ=WEEKLY;INTERVAL=2;BYDAY=TU,WE,FR;WKST=SU',
@@ -213,7 +227,7 @@ public function testWeeklyByDay2()
         );
     }
 
-    public function testWeeklyByDayByHour()
+    public function testWeeklyByDayByHour(): void
     {
         $this->parse(
             'FREQ=WEEKLY;INTERVAL=2;BYDAY=TU,WE,FR;WKST=MO;BYHOUR=8,9,10',
@@ -239,7 +253,7 @@ public function testWeeklyByDayByHour()
         );
     }
 
-    public function testWeeklyByDaySpecificHour()
+    public function testWeeklyByDaySpecificHour(): void
     {
         $this->parse(
             'FREQ=WEEKLY;INTERVAL=2;BYDAY=TU,WE,FR;WKST=SU',
@@ -262,7 +276,7 @@ public function testWeeklyByDaySpecificHour()
         );
     }
 
-    public function testMonthly()
+    public function testMonthly(): void
     {
         $this->parse(
             'FREQ=MONTHLY;INTERVAL=3;COUNT=5',
@@ -278,7 +292,7 @@ public function testMonthly()
         );
     }
 
-    public function testMonthlyEndOfMonth()
+    public function testMonthlyEndOfMonth(): void
     {
         $this->parse(
             'FREQ=MONTHLY;INTERVAL=2;COUNT=12',
@@ -301,7 +315,7 @@ public function testMonthlyEndOfMonth()
         );
     }
 
-    public function testMonthlyByMonthDay()
+    public function testMonthlyByMonthDay(): void
     {
         $this->parse(
             'FREQ=MONTHLY;INTERVAL=5;COUNT=9;BYMONTHDAY=1,31,-7',
@@ -321,7 +335,7 @@ public function testMonthlyByMonthDay()
         );
     }
 
-    public function testInvalidByMonthDay()
+    public function testInvalidByMonthDay(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -332,7 +346,7 @@ public function testInvalidByMonthDay()
     }
 
     /** @dataProvider invalidFreqByCombinationProviders */
-    public function testInvalidFreqByCombination(string $rule)
+    public function testInvalidFreqByCombination(string $rule): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -355,7 +369,7 @@ public function invalidFreqByCombinationProviders(): iterable
         ];
     }
 
-    public function testMonthlyByDay()
+    public function testMonthlyByDay(): void
     {
         $this->parse(
             'FREQ=MONTHLY;INTERVAL=2;COUNT=16;BYDAY=MO,-2TU,+1WE,3TH',
@@ -382,7 +396,7 @@ public function testMonthlyByDay()
         );
     }
 
-    public function testMonthlyByDayUntil()
+    public function testMonthlyByDayUntil(): void
     {
         $this->parse(
             'FREQ=MONTHLY;INTERVAL=1;BYDAY=WE;WKST=WE;UNTIL=20210317T000000Z',
@@ -395,11 +409,11 @@ public function testMonthlyByDayUntil()
                 '2021-03-10 00:00:00',
                 '2021-03-17 00:00:00',
             ],
-            'monthly', null, 1, new DateTime('2021-03-17')
+            'monthly', null, 1, new \DateTime('2021-03-17')
         );
     }
 
-    public function testMonthlyByDayUntilWithImpossibleNextOccurrence()
+    public function testMonthlyByDayUntilWithImpossibleNextOccurrence(): void
     {
         $this->parse(
             'FREQ=MONTHLY;INTERVAL=1;BYDAY=2WE;BYMONTHDAY=2;WKST=WE;UNTIL=20210317T000000Z',
@@ -407,11 +421,11 @@ public function testMonthlyByDayUntilWithImpossibleNextOccurrence()
             [
                 '2021-02-10 00:00:00',
             ],
-            'monthly', null, 1, new DateTime('2021-03-17')
+            'monthly', null, 1, new \DateTime('2021-03-17')
         );
     }
 
-    public function testMonthlyByDayByMonthDay()
+    public function testMonthlyByDayByMonthDay(): void
     {
         $this->parse(
             'FREQ=MONTHLY;COUNT=10;BYDAY=MO;BYMONTHDAY=1',
@@ -432,7 +446,7 @@ public function testMonthlyByDayByMonthDay()
         );
     }
 
-    public function testMonthlyByDayBySetPos()
+    public function testMonthlyByDayBySetPos(): void
     {
         $this->parse(
             'FREQ=MONTHLY;COUNT=10;BYDAY=MO,TU,WE,TH,FR;BYSETPOS=1,-1',
@@ -453,7 +467,7 @@ public function testMonthlyByDayBySetPos()
         );
     }
 
-    public function testYearly()
+    public function testYearly(): void
     {
         $this->parse(
             'FREQ=YEARLY;COUNT=10;INTERVAL=3',
@@ -474,7 +488,7 @@ public function testYearly()
         );
     }
 
-    public function testYearlyLeapYear()
+    public function testYearlyLeapYear(): void
     {
         $this->parse(
             'FREQ=YEARLY;COUNT=3',
@@ -488,7 +502,7 @@ public function testYearlyLeapYear()
         );
     }
 
-    public function testYearlyByMonth()
+    public function testYearlyByMonth(): void
     {
         $this->parse(
             'FREQ=YEARLY;COUNT=8;INTERVAL=4;BYMONTH=4,10',
@@ -507,7 +521,7 @@ public function testYearlyByMonth()
         );
     }
 
-    public function testYearlyByMonthInvalidValue1()
+    public function testYearlyByMonthInvalidValue1(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -517,7 +531,7 @@ public function testYearlyByMonthInvalidValue1()
         );
     }
 
-    public function testYearlyByMonthInvalidValue2()
+    public function testYearlyByMonthInvalidValue2(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -527,7 +541,7 @@ public function testYearlyByMonthInvalidValue2()
         );
     }
 
-    public function testYearlyByMonthManyInvalidValues()
+    public function testYearlyByMonthManyInvalidValues(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -537,7 +551,7 @@ public function testYearlyByMonthManyInvalidValues()
         );
     }
 
-    public function testYearlyByMonthEmptyValue()
+    public function testYearlyByMonthEmptyValue(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -547,7 +561,7 @@ public function testYearlyByMonthEmptyValue()
         );
     }
 
-    public function testYearlyByMonthByDay()
+    public function testYearlyByMonthByDay(): void
     {
         $this->parse(
             'FREQ=YEARLY;COUNT=8;INTERVAL=5;BYMONTH=4,10;BYDAY=1MO,-1SU',
@@ -584,7 +598,25 @@ public function testYearlyNewYearsEve()
         );
     }
 
-    public function testYearlyByYearDay()
+    public function testYearlyNewYearsDay(): void
+    {
+        $this->parse(
+            'FREQ=YEARLY;COUNT=7;INTERVAL=2;BYYEARDAY=1',
+            '2011-01-01 03:07:00',
+            [
+                '2011-01-01 03:07:00',
+                '2013-01-01 03:07:00',
+                '2015-01-01 03:07:00',
+                '2017-01-01 03:07:00',
+                '2019-01-01 03:07:00',
+                '2021-01-01 03:07:00',
+                '2023-01-01 03:07:00',
+            ],
+            'yearly', 7, 2
+        );
+    }
+
+    public function testYearlyByYearDay(): void
     {
         $this->parse(
             'FREQ=YEARLY;COUNT=7;INTERVAL=2;BYYEARDAY=190',
@@ -606,22 +638,22 @@ public function testYearlyByYearDay()
      * Regression test for #383
      * $parser->next() used to cause an infinite loop.
      */
-    public function testYearlyByYearDayImmutable()
+    public function testYearlyByYearDayImmutable(): void
     {
         $start = '2011-07-10 03:07:00';
         $rule = 'FREQ=YEARLY;COUNT=7;INTERVAL=2;BYYEARDAY=190';
         $tz = 'UTC';
 
-        $dt = new DateTimeImmutable($start, new DateTimeZone($tz));
+        $dt = new \DateTimeImmutable($start, new \DateTimeZone($tz));
         $parser = new RRuleIterator($rule, $dt);
 
         $parser->next();
 
         $item = $parser->current();
-        $this->assertEquals($item->format('Y-m-d H:i:s'), '2013-07-09 03:07:00');
+        self::assertEquals('2013-07-09 03:07:00', $item->format('Y-m-d H:i:s'));
     }
 
-    public function testYearlyByYearDayMultiple()
+    public function testYearlyByYearDayMultiple(): void
     {
         $this->parse(
             'FREQ=YEARLY;COUNT=8;INTERVAL=3;BYYEARDAY=190,301',
@@ -640,7 +672,7 @@ public function testYearlyByYearDayMultiple()
         );
     }
 
-    public function testYearlyByYearDayByDay()
+    public function testYearlyByYearDayByDay(): void
     {
         $this->parse(
             'FREQ=YEARLY;COUNT=6;BYYEARDAY=97;BYDAY=SA',
@@ -657,7 +689,7 @@ public function testYearlyByYearDayByDay()
         );
     }
 
-    public function testYearlyByYearDayNegative()
+    public function testYearlyByYearDayNegative(): void
     {
         $this->parse(
             'FREQ=YEARLY;COUNT=8;BYYEARDAY=-97,-5',
@@ -720,7 +752,56 @@ public function testFirstFourthSundayEveryOtherMonthAt830and930()
         );
     }
 
-    public function testYearlyByYearDayInvalid390()
+    /*
+     * Verifies that -365 back in the year is usually 1 Jan, but
+     * in leap years it is 2 Jan.
+     */
+    public function testYearlyByYearDayLargeNegative(): void
+    {
+        $this->parse(
+            'FREQ=YEARLY;COUNT=8;BYYEARDAY=-365',
+            '2001-01-01 14:53:11',
+            [
+                '2001-01-01 14:53:11',
+                '2002-01-01 14:53:11',
+                '2003-01-01 14:53:11',
+                '2004-01-02 14:53:11',
+                '2005-01-01 14:53:11',
+                '2006-01-01 14:53:11',
+                '2007-01-01 14:53:11',
+                '2008-01-02 14:53:11',
+            ],
+            'yearly', 8, 1
+        );
+    }
+
+    /*
+     * Verifies that -366 back in the year is 1 Jan in a leap year
+     * Interestingly, it goes back to 31 Dec of the previous year
+     * when not a leap year. The spec says that -366 is valid, and
+     * makes no mention of it being valid only in a leap year, so
+     * the behavior seems reasonable.
+     */
+    public function testYearlyByYearDayMaxNegative(): void
+    {
+        $this->parse(
+            'FREQ=YEARLY;COUNT=8;BYYEARDAY=-366',
+            '2001-01-01 14:53:11',
+            [
+                '2001-01-01 14:53:11',
+                '2001-12-31 14:53:11',
+                '2002-12-31 14:53:11',
+                '2004-01-01 14:53:11',
+                '2004-12-31 14:53:11',
+                '2005-12-31 14:53:11',
+                '2006-12-31 14:53:11',
+                '2008-01-01 14:53:11',
+            ],
+            'yearly', 8, 1
+        );
+    }
+
+    public function testYearlyByYearDayInvalid390(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -731,7 +812,7 @@ public function testYearlyByYearDayInvalid390()
         );
     }
 
-    public function testYearlyByYearDayInvalid0()
+    public function testYearlyByYearDayInvalid0(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -742,7 +823,7 @@ public function testYearlyByYearDayInvalid0()
         );
     }
 
-    public function testYearlyByDayByWeekNo()
+    public function testYearlyByDayByWeekNo(): void
     {
         $this->parse(
             'FREQ=YEARLY;COUNT=3;BYDAY=MO;BYWEEKNO=13,15,50',
@@ -756,7 +837,7 @@ public function testYearlyByDayByWeekNo()
         );
     }
 
-    public function testFastForward()
+    public function testFastForward(): void
     {
         // The idea is that we're fast-forwarding too far in the future, so
         // there will be no results left.
@@ -779,7 +860,7 @@ public function testFastForward()
      *
      * @medium
      */
-    public function testFifthTuesdayProblem()
+    public function testFifthTuesdayProblem(): void
     {
         $this->parse(
             'FREQ=MONTHLY;INTERVAL=1;UNTIL=20071030T035959Z;BYDAY=5TU',
@@ -787,7 +868,7 @@ public function testFifthTuesdayProblem()
             [
                 '2007-10-04 14:46:42',
             ],
-            'monthly', null, 1, new DateTime('2007-10-30 03:59:59')
+            'monthly', null, 1, new \DateTime('2007-10-30 03:59:59')
         );
     }
 
@@ -795,7 +876,7 @@ public function testFifthTuesdayProblem()
      * This bug came from a Fruux customer. This would result in a never-ending
      * request.
      */
-    public function testFastForwardTooFar()
+    public function testFastForwardTooFar(): void
     {
         $this->parse(
             'FREQ=WEEKLY;BYDAY=MO;UNTIL=20090704T205959Z;INTERVAL=1',
@@ -813,11 +894,11 @@ public function testFastForwardTooFar()
                 '2009-06-22 18:00:00',
                 '2009-06-29 18:00:00',
             ],
-            'weekly', null, 1, new DateTime('2009-07-04 20:59:59')
+            'weekly', null, 1, new \DateTime('2009-07-04 20:59:59')
         );
     }
 
-    public function testValidByWeekNo()
+    public function testValidByWeekNo(): void
     {
         $this->parse(
             'FREQ=YEARLY;BYWEEKNO=20;BYDAY=TU',
@@ -840,7 +921,7 @@ public function testValidByWeekNo()
         );
     }
 
-    public function testNegativeValidByWeekNo()
+    public function testNegativeValidByWeekNo(): void
     {
         $this->parse(
             'FREQ=YEARLY;BYWEEKNO=-20;BYDAY=TU,FR',
@@ -863,7 +944,7 @@ public function testNegativeValidByWeekNo()
         );
     }
 
-    public function testTwoValidByWeekNo()
+    public function testTwoValidByWeekNo(): void
     {
         $this->parse(
             'FREQ=YEARLY;BYWEEKNO=20;BYDAY=TU,FR',
@@ -886,7 +967,7 @@ public function testTwoValidByWeekNo()
         );
     }
 
-    public function testValidByWeekNoByDayDefault()
+    public function testValidByWeekNoByDayDefault(): void
     {
         $this->parse(
             'FREQ=YEARLY;BYWEEKNO=20',
@@ -909,7 +990,7 @@ public function testValidByWeekNoByDayDefault()
         );
     }
 
-    public function testMultipleValidByWeekNo()
+    public function testMultipleValidByWeekNo(): void
     {
         $this->parse(
             'FREQ=YEARLY;BYWEEKNO=20,50;BYDAY=TU,FR',
@@ -932,21 +1013,20 @@ public function testMultipleValidByWeekNo()
         );
     }
 
-    public function testInvalidByWeekNo()
+    public function testInvalidByWeekNo(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
             'FREQ=YEARLY;BYWEEKNO=54',
             '2011-05-16 00:00:00',
-            [
-            ]
+            [],
         );
     }
 
     /**
      * This also at one point caused an infinite loop. We're keeping the test.
      */
-    public function testYearlyByMonthLoop()
+    public function testYearlyByMonthLoop(): void
     {
         $this->parse(
             'FREQ=YEARLY;INTERVAL=1;UNTIL=20120203T225959Z;BYMONTH=2;BYSETPOS=1;BYDAY=SU,MO,TU,WE,TH,FR,SA',
@@ -954,17 +1034,34 @@ public function testYearlyByMonthLoop()
             [
                 '2012-02-01 15:45:00',
             ],
-            'yearly', null, 1, new DateTime('2012-02-03 22:59:59'),
+            'yearly', null, 1, new \DateTime('2012-02-03 22:59:59'),
             '2012-01-29 23:00:00'
         );
     }
 
+    /**
+     * This test can take some seconds to complete.
+     * The "large" annotation means phpunit will let it run for
+     * up to 60 seconds by default.
+     *
+     * @large
+     */
+    public function testYearlyBySetPosLoop(): void
+    {
+        $this->parse(
+            'FREQ=YEARLY;BYMONTH=5;BYSETPOS=3;BYMONTHDAY=3',
+            '2022-03-03 15:45:00',
+            [],
+            'yearly', null, 1, null, '2022-05-01'
+        );
+    }
+
     /**
      * Something, somewhere produced an ics with an interval set to 0. Because
      * this means we increase the current day (or week, month) by 0, this also
      * results in an infinite loop.
      */
-    public function testZeroInterval()
+    public function testZeroInterval(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -976,7 +1073,7 @@ public function testZeroInterval()
         );
     }
 
-    public function testInvalidFreq()
+    public function testInvalidFreq(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -986,7 +1083,7 @@ public function testInvalidFreq()
         );
     }
 
-    public function testInvalidMissingFreq()
+    public function testInvalidMissingFreq(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -996,7 +1093,7 @@ public function testInvalidMissingFreq()
         );
     }
 
-    public function testByDayBadOffset()
+    public function testByDayBadOffset(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -1006,7 +1103,7 @@ public function testByDayBadOffset()
         );
     }
 
-    public function testUntilBeginHasTimezone()
+    public function testUntilBeginHasTimezone(): void
     {
         $this->parse(
             'FREQ=WEEKLY;UNTIL=20131118T183000',
@@ -1022,13 +1119,13 @@ public function testUntilBeginHasTimezone()
                 '2013-11-11 18:30:00',
                 '2013-11-18 18:30:00',
             ],
-            'weekly', null, 1, new DateTime('2013-11-18 18:30:00-0500'),
+            'weekly', null, 1, new \DateTime('2013-11-18 18:30:00-0500'),
             null,
             'America/New_York'
         );
     }
 
-    public function testUntilBeforeDtStart()
+    public function testUntilBeforeDtStart(): void
     {
         $dtstart = '2014-08-02 00:15:00';
         $this->parse(
@@ -1037,7 +1134,7 @@ public function testUntilBeforeDtStart()
             [
                 $dtstart,
             ],
-            'daily', null, 1, new DateTime($dtstart)
+            'daily', null, 1, new \DateTime($dtstart)
         );
     }
 
@@ -1053,7 +1150,7 @@ public function testUntilAndCount()
         );
     }
 
-    public function testIgnoredStuff()
+    public function testIgnoredStuff(): void
     {
         $this->parse(
             'FREQ=DAILY;BYSECOND=1;BYMINUTE=1;COUNT=2',
@@ -1066,7 +1163,7 @@ public function testIgnoredStuff()
         );
     }
 
-    public function testMinusFifthThursday()
+    public function testMinusFifthThursday(): void
     {
         $this->parse(
             'FREQ=MONTHLY;BYDAY=-4TH,-5TH;COUNT=4',
@@ -1088,7 +1185,7 @@ public function testMinusFifthThursday()
      *
      * @large
      */
-    public function testNeverEnding()
+    public function testNeverEnding(): void
     {
         $this->parse(
             'FREQ=MONTHLY;BYDAY=2TU;BYSETPOS=2',
@@ -1103,7 +1200,7 @@ public function testNeverEnding()
         );
     }
 
-    public function testUnsupportedPart()
+    public function testUnsupportedPart(): void
     {
         $this->expectException(InvalidDataException::class);
         $this->parse(
@@ -1113,26 +1210,26 @@ public function testUnsupportedPart()
         );
     }
 
-    public function testIteratorFunctions()
+    public function testIteratorFunctions(): void
     {
-        $parser = new RRuleIterator('FREQ=DAILY', new DateTime('2014-08-02 00:00:13'));
+        $parser = new RRuleIterator('FREQ=DAILY', new \DateTime('2014-08-02 00:00:13'));
         $parser->next();
-        $this->assertEquals(
-            new DateTime('2014-08-03 00:00:13'),
+        self::assertEquals(
+            new \DateTime('2014-08-03 00:00:13'),
             $parser->current()
         );
-        $this->assertEquals(
+        self::assertEquals(
             1,
             $parser->key()
         );
 
         $parser->rewind();
 
-        $this->assertEquals(
-            new DateTime('2014-08-02 00:00:13'),
+        self::assertEquals(
+            new \DateTime('2014-08-02 00:00:13'),
             $parser->current()
         );
-        $this->assertEquals(
+        self::assertEquals(
             0,
             $parser->key()
         );
@@ -1140,17 +1237,17 @@ public function testIteratorFunctions()
 
     public function parse(
         $rule,
-        $start,
-        $expected,
+        string $start,
+        array $expected,
         $expectedFreq = null,
         $expectedCount = null,
         $expectedInterval = null,
         $expectedUntil = null,
-        $fastForward = null,
-        $tz = 'UTC',
-        $runTillTheEnd = false
-    ) {
-        $dt = new DateTime($start, new DateTimeZone($tz));
+        string $fastForward = null,
+        string $tz = 'UTC',
+        bool $runTillTheEnd = false
+    ): void {
+        $dt = new \DateTime($start, new \DateTimeZone($tz));
         $parser = new RRuleIterator($rule, $dt);
 
         $this->assertEquals($expectedFreq, $parser->getFrequency());
@@ -1159,7 +1256,7 @@ public function parse(
         $this->assertEquals($expectedUntil, $parser->getUntil());
 
         if ($fastForward) {
-            $parser->fastForward(new DateTime($fastForward));
+            $parser->fastForward(new \DateTime($fastForward));
         }
 
         $result = [];
@@ -1173,7 +1270,7 @@ public function parse(
             $parser->next();
         }
 
-        $this->assertEquals(
+        self::assertEquals(
             $expected,
             $result
         );
diff --git a/tests/VObject/SlashRTest.php b/tests/VObject/SlashRTest.php
index 688563af1..8f968d3c9 100644
--- a/tests/VObject/SlashRTest.php
+++ b/tests/VObject/SlashRTest.php
@@ -10,10 +10,10 @@
  */
 class SlashRTest extends TestCase
 {
-    public function testEncode()
+    public function testEncode(): void
     {
         $vcal = new Component\VCalendar();
         $prop = $vcal->add('test', "abc\r\ndef");
-        $this->assertEquals("TEST:abc\\ndef\r\n", $prop->serialize());
+        self::assertEquals("TEST:abc\\ndef\r\n", $prop->serialize());
     }
 }
diff --git a/tests/VObject/Splitter/ICalendarTest.php b/tests/VObject/Splitter/ICalendarTest.php
index 2788b96d6..f5428e937 100644
--- a/tests/VObject/Splitter/ICalendarTest.php
+++ b/tests/VObject/Splitter/ICalendarTest.php
@@ -8,14 +8,14 @@
 
 class ICalendarTest extends TestCase
 {
-    protected $version;
+    protected string $version;
 
     public function setUp(): void
     {
         $this->version = VObject\Version::VERSION;
     }
 
-    public function createStream($data)
+    public function createStream(string $data)
     {
         $stream = fopen('php://memory', 'r+');
         fwrite($stream, $data);
@@ -24,7 +24,7 @@ public function createStream($data)
         return $stream;
     }
 
-    public function testICalendarImportValidEvent()
+    public function testICalendarImportValidEvent(): void
     {
         $data = <<<EOT
 BEGIN:VCALENDAR
@@ -43,10 +43,10 @@ public function testICalendarImportValidEvent()
         while ($object = $objects->getNext()) {
             $return .= $object->serialize();
         }
-        $this->assertEquals([], VObject\Reader::read($return)->validate());
+        self::assertEquals([], VObject\Reader::read($return)->validate());
     }
 
-    public function testICalendarImportWrongType()
+    public function testICalendarImportWrongType(): void
     {
         $this->expectException(ParseException::class);
         $data = <<<EOT
@@ -59,10 +59,10 @@ public function testICalendarImportWrongType()
 EOT;
         $tempFile = $this->createStream($data);
 
-        $objects = new ICalendar($tempFile);
+        new ICalendar($tempFile);
     }
 
-    public function testICalendarImportEndOfData()
+    public function testICalendarImportEndOfData(): void
     {
         $data = <<<EOT
 BEGIN:VCALENDAR
@@ -80,19 +80,19 @@ public function testICalendarImportEndOfData()
         while ($object = $objects->getNext()) {
             $return .= $object->serialize();
         }
-        $this->assertNull($object = $objects->getNext());
+        self::assertNull($objects->getNext());
     }
 
-    public function testICalendarImportInvalidEvent()
+    public function testICalendarImportInvalidEvent(): void
     {
         $this->expectException(ParseException::class);
         $data = <<<EOT
 EOT;
         $tempFile = $this->createStream($data);
-        $objects = new ICalendar($tempFile);
+        new ICalendar($tempFile);
     }
 
-    public function testICalendarImportMultipleValidEvents()
+    public function testICalendarImportMultipleValidEvents(): void
     {
         $event[] = <<<EOT
 BEGIN:VEVENT
@@ -136,13 +136,13 @@ public function testICalendarImportMultipleValidEvents()
 
             $return .= $object->serialize();
             $expected = str_replace("\n", "\r\n", $expected);
-            $this->assertEquals($expected, $object->serialize());
+            self::assertEquals($expected, $object->serialize());
             ++$i;
         }
-        $this->assertEquals([], VObject\Reader::read($return)->validate());
+        self::assertEquals([], VObject\Reader::read($return)->validate());
     }
 
-    public function testICalendarImportEventWithoutUID()
+    public function testICalendarImportEventWithoutUID(): void
     {
         $data = <<<EOT
 BEGIN:VCALENDAR
@@ -174,11 +174,11 @@ function ($item) { return $item['message']; },
             );
             $this->fail('Validation errors: '.implode("\n", $messages));
         } else {
-            $this->assertEquals([], $messages);
+            self::assertEquals([], $messages);
         }
     }
 
-    public function testICalendarImportMultipleVTIMEZONESAndMultipleValidEvents()
+    public function testICalendarImportMultipleVTIMEZONESAndMultipleValidEvents(): void
     {
         $timezones = <<<EOT
 BEGIN:VTIMEZONE
@@ -269,15 +269,15 @@ public function testICalendarImportMultipleVTIMEZONESAndMultipleValidEvents()
 EOT;
             $expected = str_replace("\n", "\r\n", $expected);
 
-            $this->assertEquals($expected, $object->serialize());
+            self::assertEquals($expected, $object->serialize());
             $return .= $object->serialize();
             ++$i;
         }
 
-        $this->assertEquals([], VObject\Reader::read($return)->validate());
+        self::assertEquals([], VObject\Reader::read($return)->validate());
     }
 
-    public function testICalendarImportWithOutVTIMEZONES()
+    public function testICalendarImportWithOutVTIMEZONES(): void
     {
         $data = <<<EOT
 BEGIN:VCALENDAR
@@ -315,6 +315,6 @@ public function testICalendarImportWithOutVTIMEZONES()
         }
 
         $messages = VObject\Reader::read($return)->validate();
-        $this->assertEquals([], $messages);
+        self::assertEquals([], $messages);
     }
 }
diff --git a/tests/VObject/Splitter/VCardTest.php b/tests/VObject/Splitter/VCardTest.php
index 1402b5094..7ebb07b95 100644
--- a/tests/VObject/Splitter/VCardTest.php
+++ b/tests/VObject/Splitter/VCardTest.php
@@ -16,7 +16,7 @@ public function createStream($data)
         return $stream;
     }
 
-    public function testVCardImportValidVCard()
+    public function testVCardImportValidVCard(): void
     {
         $data = <<<EOT
 BEGIN:VCARD
@@ -31,10 +31,10 @@ public function testVCardImportValidVCard()
         while ($objects->getNext()) {
             ++$count;
         }
-        $this->assertEquals(1, $count);
+        self::assertEquals(1, $count);
     }
 
-    public function testVCardImportWrongType()
+    public function testVCardImportWrongType(): void
     {
         $this->expectException(ParseException::class);
         $event[] = <<<EOT
@@ -64,11 +64,11 @@ public function testVCardImportWrongType()
 
         $splitter = new VCard($tempFile);
 
-        while ($object = $splitter->getNext()) {
+        while ($splitter->getNext()) {
         }
     }
 
-    public function testVCardImportValidVCardsWithCategories()
+    public function testVCardImportValidVCardsWithCategories(): void
     {
         $data = <<<EOT
 BEGIN:VCARD
@@ -93,13 +93,13 @@ public function testVCardImportValidVCardsWithCategories()
         $splitter = new VCard($tempFile);
 
         $count = 0;
-        while ($object = $splitter->getNext()) {
+        while ($splitter->getNext()) {
             ++$count;
         }
-        $this->assertEquals(4, $count);
+        self::assertEquals(4, $count);
     }
 
-    public function testVCardImportVCardNoComponent()
+    public function testVCardImportVCardNoComponent(): void
     {
         $this->expectException(ParseException::class);
         $data = <<<EOT
@@ -116,11 +116,11 @@ public function testVCardImportVCardNoComponent()
 
         $this->expectException(ParseException::class);
         $this->expectExceptionMessage('Invalid MimeDir file. Unexpected component: "BEGIN:VCARD" in document type VCARD');
-        while ($object = $splitter->getNext()) {
+        while ($splitter->getNext()) {
         }
     }
 
-    public function testVCardImportQuotedPrintableOptionForgivingLeading()
+    public function testVCardImportQuotedPrintableOptionForgivingLeading(): void
     {
         $data = <<<EOT
 BEGIN:VCARD
@@ -137,13 +137,13 @@ public function testVCardImportQuotedPrintableOptionForgivingLeading()
         $splitter = new VCard($tempFile, \Sabre\VObject\Parser\Parser::OPTION_FORGIVING);
 
         $count = 0;
-        while ($object = $splitter->getNext()) {
+        while ($splitter->getNext()) {
             ++$count;
         }
-        $this->assertEquals(2, $count);
+        self::assertEquals(2, $count);
     }
 
-    public function testVCardImportEndOfData()
+    public function testVCardImportEndOfData(): void
     {
         $data = <<<EOT
 BEGIN:VCARD
@@ -153,12 +153,12 @@ public function testVCardImportEndOfData()
         $tempFile = $this->createStream($data);
 
         $objects = new VCard($tempFile);
-        $object = $objects->getNext();
+        $objects->getNext();
 
-        $this->assertNull($objects->getNext());
+        self::assertNull($objects->getNext());
     }
 
-    public function testVCardImportCheckInvalidArgumentException()
+    public function testVCardImportCheckInvalidArgumentException(): void
     {
         $this->expectException(ParseException::class);
         $data = <<<EOT
@@ -172,7 +172,7 @@ public function testVCardImportCheckInvalidArgumentException()
         }
     }
 
-    public function testVCardImportMultipleValidVCards()
+    public function testVCardImportMultipleValidVCards(): void
     {
         $data = <<<EOT
 BEGIN:VCARD
@@ -190,10 +190,10 @@ public function testVCardImportMultipleValidVCards()
         while ($objects->getNext()) {
             ++$count;
         }
-        $this->assertEquals(2, $count);
+        self::assertEquals(2, $count);
     }
 
-    public function testImportMultipleSeparatedWithNewLines()
+    public function testImportMultipleSeparatedWithNewLines(): void
     {
         $data = <<<EOT
 BEGIN:VCARD
@@ -214,10 +214,10 @@ public function testImportMultipleSeparatedWithNewLines()
         while ($objects->getNext()) {
             ++$count;
         }
-        $this->assertEquals(2, $count);
+        self::assertEquals(2, $count);
     }
 
-    public function testVCardImportVCardWithoutUID()
+    public function testVCardImportVCardWithoutUID(): void
     {
         $data = <<<EOT
 BEGIN:VCARD
@@ -232,6 +232,6 @@ public function testVCardImportVCardWithoutUID()
             ++$count;
         }
 
-        $this->assertEquals(1, $count);
+        self::assertEquals(1, $count);
     }
 }
diff --git a/tests/VObject/StringUtilTest.php b/tests/VObject/StringUtilTest.php
index c614f6aac..6d6b9b05e 100644
--- a/tests/VObject/StringUtilTest.php
+++ b/tests/VObject/StringUtilTest.php
@@ -6,45 +6,46 @@
 
 class StringUtilTest extends TestCase
 {
-    public function testNonUTF8()
+    public function testNonUTF8(): void
     {
-        $string = StringUtil::isUTF8(chr(0xbf));
+        $string = StringUtil::isUTF8(chr(0xBF));
 
-        $this->assertEquals(false, $string);
+        self::assertEquals(false, $string);
     }
 
-    public function testIsUTF8()
+    public function testIsUTF8(): void
     {
         $string = StringUtil::isUTF8('I 💚 SabreDAV');
 
-        $this->assertEquals(true, $string);
+        self::assertEquals(true, $string);
     }
 
-    public function testUTF8ControlChar()
+    public function testUTF8ControlChar(): void
     {
         $string = StringUtil::isUTF8(chr(0x00));
 
-        $this->assertEquals(false, $string);
+        self::assertEquals(false, $string);
     }
 
-    public function testConvertToUTF8nonUTF8()
+    public function testConvertToUTF8nonUTF8(): void
     {
-        $string = StringUtil::convertToUTF8(chr(0xbf));
+        // 0xBF is an ASCII upside-down question mark
+        $string = StringUtil::convertToUTF8(chr(0xBF));
 
-        $this->assertEquals(utf8_encode(chr(0xbf)), $string);
+        self::assertEquals(mb_convert_encoding(chr(0xBF), 'UTF-8', 'ISO-8859-1'), $string);
     }
 
-    public function testConvertToUTF8IsUTF8()
+    public function testConvertToUTF8IsUTF8(): void
     {
         $string = StringUtil::convertToUTF8('I 💚 SabreDAV');
 
-        $this->assertEquals('I 💚 SabreDAV', $string);
+        self::assertEquals('I 💚 SabreDAV', $string);
     }
 
-    public function testConvertToUTF8ControlChar()
+    public function testConvertToUTF8ControlChar(): void
     {
         $string = StringUtil::convertToUTF8(chr(0x00));
 
-        $this->assertEquals('', $string);
+        self::assertEquals('', $string);
     }
 }
diff --git a/tests/VObject/TimeZoneUtilTest.php b/tests/VObject/TimeZoneUtilTest.php
index ff409a1ff..1069b437a 100644
--- a/tests/VObject/TimeZoneUtilTest.php
+++ b/tests/VObject/TimeZoneUtilTest.php
@@ -14,11 +14,11 @@ public function setUp(): void
     /**
      * @dataProvider getMapping
      */
-    public function testCorrectTZ($timezoneName)
+    public function testCorrectTZ(string $timezoneName): void
     {
         try {
             $tz = new \DateTimeZone($timezoneName);
-            $this->assertInstanceOf('DateTimeZone', $tz);
+            self::assertInstanceOf('DateTimeZone', $tz);
         } catch (\Exception $e) {
             if (false !== strpos($e->getMessage(), 'Unknown or bad timezone')) {
                 $this->markTestSkipped($timezoneName.' is not (yet) supported in this PHP version. Update pecl/timezonedb');
@@ -28,14 +28,14 @@ public function testCorrectTZ($timezoneName)
         }
     }
 
-    public function getMapping()
+    public function getMapping(): array
     {
         $map = array_merge(
             include __DIR__.'/../../lib/timezonedata/windowszones.php',
             include __DIR__.'/../../lib/timezonedata/lotuszones.php',
             include __DIR__.'/../../lib/timezonedata/exchangezones.php',
             include __DIR__.'/../../lib/timezonedata/php-workaround.php',
-            include __DIR__.'/../../lib/timezonedata/extrazones.php'
+            include __DIR__.'/../../lib/timezonedata/extrazones.php',
         );
 
         // PHPUNit requires an array of arrays
@@ -50,15 +50,15 @@ function ($value) {
     /**
      * @dataProvider getMapping
      */
-    public function testSlashTZ($timezonename)
+    public function testSlashTZ($timezonename): void
     {
         $slashTimezone = '/'.$timezonename;
         $expected = TimeZoneUtil::getTimeZone($timezonename)->getName();
         $actual = TimeZoneUtil::getTimeZone($slashTimezone)->getName();
-        $this->assertEquals($expected, $actual);
+        self::assertEquals($expected, $actual);
     }
 
-    public function testExchangeMap()
+    public function testExchangeMap(): void
     {
         $vobj = <<<HI
 BEGIN:VCALENDAR
@@ -95,10 +95,10 @@ public function testExchangeMap()
         $tz = TimeZoneUtil::getTimeZone('foo', Reader::read($vobj));
         $ex = new \DateTimeZone('Europe/Lisbon');
 
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function testWhetherMicrosoftIsStillInsane()
+    public function testWhetherMicrosoftIsStillInsane(): void
     {
         $vobj = <<<HI
 BEGIN:VCALENDAR
@@ -120,10 +120,10 @@ public function testWhetherMicrosoftIsStillInsane()
         $tz = TimeZoneUtil::getTimeZone('(GMT+01.00) Sarajevo/Warsaw/Zagreb', Reader::read($vobj));
         $ex = new \DateTimeZone('Europe/Sarajevo');
 
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function testUnknownExchangeId()
+    public function testUnknownExchangeId(): void
     {
         $vobj = <<<HI
 BEGIN:VCALENDAR
@@ -160,69 +160,80 @@ public function testUnknownExchangeId()
 
         $tz = TimeZoneUtil::getTimeZone('foo', Reader::read($vobj));
         $ex = new \DateTimeZone(date_default_timezone_get());
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function testEmptyTimeZone()
+    public function testEmptyTimeZone(): void
     {
         $tz = TimeZoneUtil::getTimeZone('');
         $ex = new \DateTimeZone('UTC');
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function testWindowsTimeZone()
+    public function testWindowsTimeZone(): void
     {
         $tz = TimeZoneUtil::getTimeZone('Eastern Standard Time');
         $ex = new \DateTimeZone('America/New_York');
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function testLowerCaseTimeZone()
+    public function testLowerCaseTimeZone(): void
     {
         $tz = TimeZoneUtil::getTimeZone('mountain time (us & canada)');
         $ex = new \DateTimeZone('America/Denver');
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function testDeprecatedTimeZone()
+    public function testDeprecatedTimeZone(): void
     {
         // Deprecated in 2022b
         $tz = TimeZoneUtil::getTimeZone('Europe/Kiev');
         $ex = new \DateTimeZone('Europe/Kiev');
-        $this->assertSame($ex->getName(), $tz->getName());
+        self::assertSame($ex->getName(), $tz->getName());
     }
 
-    public function testDeprecatedUnsupportedTimeZone()
+    public function testDeprecatedUnsupportedTimeZone(): void
     {
         // Deprecated and unsupported
         $tz = TimeZoneUtil::getTimeZone('America/Godthab');
         $ex = new \DateTimeZone('America/Godthab');
-        $this->assertNotSame($ex->getName(), $tz->getName());
+        self::assertNotSame($ex->getName(), $tz->getName());
     }
 
     /**
      * @dataProvider getPHPTimeZoneIdentifiers
      */
-    public function testTimeZoneIdentifiers($tzid)
+    public function testTimeZoneIdentifiers(string $tzid): void
     {
         $tz = TimeZoneUtil::getTimeZone($tzid);
         $ex = new \DateTimeZone($tzid);
 
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
     /**
      * @dataProvider getPHPTimeZoneBCIdentifiers
      */
-    public function testTimeZoneBCIdentifiers($tzid)
-    {
+    public function testTimeZoneBCIdentifiers(string $tzid): void
+    {
+        /*
+         * A regression was introduced in PHP 8.1.14 and 8.2.1
+         * Timezone ids containing a "+" like "GMT+10" do not work.
+         * See https://github.com/php/php-src/issues/10218
+         * The regression should be fixed in the next patch releases of PHP
+         * that should be released in Feb 2023.
+         */
+        $versionOfPHP = \phpversion();
+        if ((('8.1.14' == $versionOfPHP) || ('8.2.1' == $versionOfPHP)) && \str_contains($tzid, '+')) {
+            $this->markTestSkipped("Timezone ids containing '+' do not work on PHP $versionOfPHP");
+        }
         $tz = TimeZoneUtil::getTimeZone($tzid);
         $ex = new \DateTimeZone($tzid);
 
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function getPHPTimeZoneIdentifiers()
+    public function getPHPTimeZoneIdentifiers(): array
     {
         // PHPUNit requires an array of arrays
         return array_map(
@@ -231,12 +242,12 @@ function ($value) {
             },
             // FIXME remove the filter after finishing timezone migration
             array_filter(\DateTimeZone::listIdentifiers(), static function (string $timezone) {
-                return $timezone !== 'Europe/Kyiv';
+                return 'Europe/Kyiv' !== $timezone;
             })
         );
     }
 
-    public function getPHPTimeZoneBCIdentifiers()
+    public function getPHPTimeZoneBCIdentifiers(): array
     {
         // PHPUNit requires an array of arrays
         return array_map(
@@ -247,13 +258,12 @@ function ($value) {
         );
     }
 
-    public function testKyivTimezone()
+    public function testKyivTimezone(): void
     {
-
-        $this->assertSame('Europe/Kiev', TimeZoneUtil::getTimeZone('Europe/Kyiv')->getName());
+        self::assertSame('Europe/Kiev', TimeZoneUtil::getTimeZone('Europe/Kyiv')->getName());
     }
 
-    public function testTimezoneOffset()
+    public function testTimezoneOffset(): void
     {
         $tz = TimeZoneUtil::getTimeZone('GMT-0400', null, true);
 
@@ -262,16 +272,16 @@ public function testTimezoneOffset()
         } else {
             $ex = new \DateTimeZone('Etc/GMT-4');
         }
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function testTimezoneFail()
+    public function testTimezoneFail(): void
     {
-        $this->expectException(\InvalidArgumentException::class);
-        $tz = TimeZoneUtil::getTimeZone('FooBar', null, true);
+        self::expectException(\InvalidArgumentException::class);
+        TimeZoneUtil::getTimeZone('FooBar', null, true);
     }
 
-    public function testFallBack()
+    public function testFallBack(): void
     {
         $vobj = <<<HI
 BEGIN:VCALENDAR
@@ -306,10 +316,10 @@ public function testFallBack()
 
         $tz = TimeZoneUtil::getTimeZone('foo', Reader::read($vobj));
         $ex = new \DateTimeZone(date_default_timezone_get());
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function testLjubljanaBug()
+    public function testLjubljanaBug(): void
     {
         $vobj = <<<HI
 BEGIN:VCALENDAR
@@ -352,10 +362,10 @@ public function testLjubljanaBug()
 
         $tz = TimeZoneUtil::getTimeZone('/freeassociation.sourceforge.net/Tzfile/Europe/Ljubljana', Reader::read($vobj));
         $ex = new \DateTimeZone('Europe/Ljubljana');
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function testWeirdSystemVLICs()
+    public function testWeirdSystemVLICs(): void
     {
         $vobj = <<<HI
 BEGIN:VCALENDAR
@@ -400,31 +410,31 @@ public function testWeirdSystemVLICs()
 
         $tz = TimeZoneUtil::getTimeZone('/freeassociation.sourceforge.net/Tzfile/SystemV/EST5EDT', Reader::read($vobj), true);
         $ex = new \DateTimeZone('America/New_York');
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function testPrefixedOffsetExchangeIdentifier()
+    public function testPrefixedOffsetExchangeIdentifier(): void
     {
         $tz = TimeZoneUtil::getTimeZone('(UTC-05:00) Eastern Time (US & Canada)');
         $ex = new \DateTimeZone('America/New_York');
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function testMicrosoftMap()
+    public function testMicrosoftMap(): void
     {
         $tz = TimeZoneUtil::getTimeZone('tzone://Microsoft/Utc', null, true);
         $ex = new \DateTimeZone('UTC');
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
     /**
      * @dataProvider unSupportTimezoneProvider
      */
-    public function testPHPUnSupportTimeZone(string $origin, string $expected)
+    public function testPHPUnSupportTimeZone(string $origin, string $expected): void
     {
         $tz = TimeZoneUtil::getTimeZone($origin, null, true);
         $ex = new \DateTimeZone($expected);
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
     public function unSupportTimezoneProvider(): iterable
@@ -474,12 +484,12 @@ public function unSupportTimezoneProvider(): iterable
             'expected' => 'Asia/Dubai',
         ];
 
-        if (($handle = fopen(__DIR__ . "/microsoft-timezones-confluence.csv", "r")) !== FALSE) {
+        if (($handle = fopen(__DIR__.'/microsoft-timezones-confluence.csv', 'r')) !== false) {
             $data = fgetcsv($handle);
-            while (($data = fgetcsv($handle)) !== FALSE) {
+            while (($data = fgetcsv($handle)) !== false) {
                 yield $data[0] => [
                     'origin' => $data[0],
-                    'expected' => $data[2] !== '' ? $data[2] : $data[1],
+                    'expected' => '' !== $data[2] ? $data[2] : $data[1],
                 ];
             }
             fclose($handle);
@@ -489,11 +499,11 @@ public function unSupportTimezoneProvider(): iterable
     /**
      * @dataProvider offsetTimeZoneProvider
      */
-    public function testOffsetTimeZones(string $origin, string $expected)
+    public function testOffsetTimeZones(string $origin, string $expected): void
     {
         $tz = TimeZoneUtil::getTimeZone($origin, null, true);
         $ex = new \DateTimeZone($expected);
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
     public function offsetTimeZoneProvider(): iterable
@@ -522,11 +532,11 @@ public function offsetTimeZoneProvider(): iterable
     /**
      * @dataProvider letterCaseTimeZoneProvider
      */
-    public function testDifferentLetterCaseTimeZone(string $origin, string $expected)
+    public function testDifferentLetterCaseTimeZone(string $origin, string $expected): void
     {
         $tz = TimeZoneUtil::getTimeZone($origin, null, true);
         $ex = new \DateTimeZone($expected);
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
     public function letterCaseTimeZoneProvider(): iterable
@@ -555,11 +565,11 @@ public function letterCaseTimeZoneProvider(): iterable
     /**
      * @dataProvider outlookCitiesProvider
      */
-    public function testOutlookCities(string $origin, bool $failIfUncertain, string $expected)
+    public function testOutlookCities(string $origin, bool $failIfUncertain, string $expected): void
     {
         $tz = TimeZoneUtil::getTimeZone($origin, null, $failIfUncertain);
         $ex = new \DateTimeZone($expected);
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
     public function outlookCitiesProvider(): iterable
@@ -592,11 +602,11 @@ public function outlookCitiesProvider(): iterable
     /**
      * @dataProvider versionTzProvider
      */
-    public function testVersionTz(string $origin, bool $failIfUncertain, string $expected)
+    public function testVersionTz(string $origin, bool $failIfUncertain, string $expected): void
     {
         $tz = TimeZoneUtil::getTimeZone($origin, null, $failIfUncertain);
         $ex = new \DateTimeZone($expected);
-        $this->assertEquals($ex->getName(), $tz->getName());
+        self::assertEquals($ex->getName(), $tz->getName());
     }
 
     public function versionTzProvider(): iterable
@@ -614,7 +624,7 @@ public function versionTzProvider(): iterable
         ];
     }
 
-    public function testCustomizedTimeZone()
+    public function testCustomizedTimeZone(): void
     {
         $ics = <<<ICS
 BEGIN:VCALENDAR
@@ -653,26 +663,26 @@ public function testCustomizedTimeZone()
 ICS;
 
         $tz = TimeZoneUtil::getTimeZone('Customized Time Zone', Reader::read($ics));
-        $this->assertNotSame('Customized Time Zone', $tz->getName());
+        self::assertNotSame('Customized Time Zone', $tz->getName());
         $start = new \DateTimeImmutable('2022-04-25');
-        $this->assertSame(10 * 60 * 60, $tz->getOffset($start));
+        self::assertSame(10 * 60 * 60, $tz->getOffset($start));
 
         $start = new \DateTimeImmutable('2022-11-10');
-        $this->assertSame(11 * 60 * 60, $tz->getOffset($start));
+        self::assertSame(11 * 60 * 60, $tz->getOffset($start));
     }
 
-    public function testCustomizedTimeZoneWithoutDaylight()
+    public function testCustomizedTimeZoneWithoutDaylight(): void
     {
         $ics = $this->getCustomizedICS();
         $tz = TimeZoneUtil::getTimeZone('Customized Time Zone', Reader::read($ics));
-        $this->assertSame('Asia/Brunei', $tz->getName());
+        self::assertSame('Asia/Brunei', $tz->getName());
         $start = new \DateTimeImmutable('2022-04-25');
-        $this->assertSame(8 * 60 * 60, $tz->getOffset($start));
+        self::assertSame(8 * 60 * 60, $tz->getOffset($start));
     }
 
-    public function testCustomizedTimeZoneFlag()
+    public function testCustomizedTimeZoneFlag(): void
     {
-        $this->expectException(\InvalidArgumentException::class);
+        self::expectException(\InvalidArgumentException::class);
         $ics = $this->getCustomizedICS();
         $vobject = Reader::read($ics);
         $vobject->VEVENT->DTSTART->getDateTime(null, false);
diff --git a/tests/VObject/UUIDUtilTest.php b/tests/VObject/UUIDUtilTest.php
index 579928f38..170107b30 100644
--- a/tests/VObject/UUIDUtilTest.php
+++ b/tests/VObject/UUIDUtilTest.php
@@ -6,18 +6,18 @@
 
 class UUIDUtilTest extends TestCase
 {
-    public function testValidateUUID()
+    public function testValidateUUID(): void
     {
-        $this->assertTrue(
+        self::assertTrue(
             UUIDUtil::validateUUID('11111111-2222-3333-4444-555555555555')
         );
-        $this->assertFalse(
+        self::assertFalse(
             UUIDUtil::validateUUID(' 11111111-2222-3333-4444-555555555555')
         );
-        $this->assertTrue(
+        self::assertTrue(
             UUIDUtil::validateUUID('ffffffff-2222-3333-4444-555555555555')
         );
-        $this->assertFalse(
+        self::assertFalse(
             UUIDUtil::validateUUID('fffffffg-2222-3333-4444-555555555555')
         );
     }
@@ -25,9 +25,9 @@ public function testValidateUUID()
     /**
      * @depends testValidateUUID
      */
-    public function testGetUUID()
+    public function testGetUUID(): void
     {
-        $this->assertTrue(
+        self::assertTrue(
             UUIDUtil::validateUUID(
                 UUIDUtil::getUUID()
             )
diff --git a/tests/VObject/VCard21Test.php b/tests/VObject/VCard21Test.php
index 9dd07288e..d091e35d0 100644
--- a/tests/VObject/VCard21Test.php
+++ b/tests/VObject/VCard21Test.php
@@ -9,7 +9,7 @@
  */
 class VCard21Test extends TestCase
 {
-    public function testPropertyWithNoName()
+    public function testPropertyWithNoName(): void
     {
         $input = <<<VCF
 BEGIN:VCARD\r
@@ -22,10 +22,10 @@ public function testPropertyWithNoName()
         $vobj = Reader::read($input);
         $output = $vobj->serialize();
 
-        $this->assertEquals($input, $output);
+        self::assertEquals($input, $output);
     }
 
-    public function testPropertyPadValueCount()
+    public function testPropertyPadValueCount(): void
     {
         $input = <<<VCF
 BEGIN:VCARD
@@ -46,6 +46,6 @@ public function testPropertyPadValueCount()
 
 VCF;
 
-        $this->assertEquals($expected, $output);
+        self::assertEquals($expected, $output);
     }
 }
diff --git a/tests/VObject/VCardConverterTest.php b/tests/VObject/VCardConverterTest.php
index ae2b10bd5..949a102a7 100644
--- a/tests/VObject/VCardConverterTest.php
+++ b/tests/VObject/VCardConverterTest.php
@@ -3,12 +3,16 @@
 namespace Sabre\VObject;
 
 use PHPUnit\Framework\TestCase;
+use Sabre\VObject\Component\VCard;
 
 class VCardConverterTest extends TestCase
 {
-    use \Sabre\VObject\PHPUnitAssertions;
+    use PHPUnitAssertions;
 
-    public function testConvert30to40()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testConvert30to40(): void
     {
         $input = <<<IN
 BEGIN:VCARD
@@ -41,16 +45,20 @@ public function testConvert30to40()
 END:VCARD
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD40);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
     }
 
-    public function testConvert40to40()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testConvert40to40(): void
     {
         $input = <<<IN
 BEGIN:VCARD
@@ -78,16 +86,20 @@ public function testConvert40to40()
 
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD40);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
     }
 
-    public function testConvert21to40()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testConvert21to40(): void
     {
         $input = <<<IN
 BEGIN:VCARD
@@ -116,16 +128,20 @@ public function testConvert21to40()
 
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD40);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
     }
 
-    public function testConvert30to30()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testConvert30to30(): void
     {
         $input = <<<IN
 BEGIN:VCARD
@@ -155,16 +171,20 @@ public function testConvert30to30()
 
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD30);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
     }
 
-    public function testConvert40to30()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testConvert40to30(): void
     {
         $input = <<<IN
 BEGIN:VCARD
@@ -195,22 +215,28 @@ public function testConvert40to30()
 
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD30);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
     }
 
-    public function testConvertGroupCard()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testConvertGroupCard(): void
     {
         $input = <<<IN
 BEGIN:VCARD
 VERSION:3.0
 PRODID:foo
 X-ADDRESSBOOKSERVER-KIND:GROUP
+X-ADDRESSBOOKSERVER-MEMBER:mailto:someone@example.com
+X-ADDRESSBOOKSERVER-MEMBER:mailto:sometwo@example.com
 END:VCARD
 
 IN;
@@ -219,14 +245,17 @@ public function testConvertGroupCard()
 BEGIN:VCARD
 VERSION:4.0
 KIND:GROUP
+MEMBER:mailto:someone@example.com
+MEMBER:mailto:sometwo@example.com
 END:VCARD
 
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD40);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
@@ -236,20 +265,26 @@ public function testConvertGroupCard()
 BEGIN:VCARD
 VERSION:3.0
 X-ADDRESSBOOKSERVER-KIND:GROUP
+X-ADDRESSBOOKSERVER-MEMBER:mailto:someone@example.com
+X-ADDRESSBOOKSERVER-MEMBER:mailto:sometwo@example.com
 END:VCARD
 
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD30);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
     }
 
-    public function testBDAYConversion()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testBDAYConversion(): void
     {
         $input = <<<IN
 BEGIN:VCARD
@@ -268,10 +303,11 @@ public function testBDAYConversion()
 
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD40);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
@@ -285,16 +321,20 @@ public function testBDAYConversion()
 
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD30);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
     }
 
-    public function testUnknownSourceVCardVersion()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testUnknownSourceVCardVersion(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $input = <<<IN
@@ -314,11 +354,15 @@ public function testUnknownSourceVCardVersion()
 
 IN;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard->convert(Document::VCARD40);
     }
 
-    public function testUnknownTargetVCardVersion()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testUnknownTargetVCardVersion(): void
     {
         $this->expectException(\InvalidArgumentException::class);
         $input = <<<IN
@@ -329,11 +373,15 @@ public function testUnknownTargetVCardVersion()
 
 IN;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard->convert(Document::VCARD21);
     }
 
-    public function testConvertIndividualCard()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testConvertIndividualCard(): void
     {
         $input = <<<IN
 BEGIN:VCARD
@@ -351,10 +399,11 @@ public function testConvertIndividualCard()
 
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD30);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
@@ -367,16 +416,20 @@ public function testConvertIndividualCard()
 
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD40);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
     }
 
-    public function testAnniversary()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testAnniversary(): void
     {
         $input = <<<IN
 BEGIN:VCARD
@@ -396,10 +449,11 @@ public function testAnniversary()
 
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD30);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
@@ -413,16 +467,20 @@ public function testAnniversary()
             $input,
         ];
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD40);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
     }
 
-    public function testMultipleAnniversaries()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testMultipleAnniversaries(): void
     {
         $input = <<<IN
 BEGIN:VCARD
@@ -450,10 +508,11 @@ public function testMultipleAnniversaries()
 
 OUT;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD30);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
@@ -467,16 +526,20 @@ public function testMultipleAnniversaries()
             $input,
         ];
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD40);
 
-        $this->assertVObjectEqualsVObject(
+        self::assertVObjectEqualsVObject(
             $output,
             $vcard
         );
     }
 
-    public function testNoLabel()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testNoLabel(): void
     {
         $input = <<<VCF
 BEGIN:VCARD
@@ -491,10 +554,12 @@ public function testNoLabel()
 
         $vcard = Reader::read($input);
 
-        $this->assertInstanceOf(Component\VCard::class, $vcard);
+        self::assertInstanceOf(Component\VCard::class, $vcard);
+        /** @var VCard $vcard */
         $vcard = $vcard->convert(Document::VCARD40);
         $vcard = $vcard->serialize();
 
+        /** @var VCard $converted */
         $converted = Reader::read($vcard);
         $converted->validate();
 
@@ -512,10 +577,13 @@ public function testNoLabel()
 
 VCF;
 
-        $this->assertEquals($expected, str_replace("\r", '', $vcard));
+        self::assertEquals($expected, str_replace("\r", '', $vcard));
     }
 
-    public function testPhoneNumberValueTypeGetsRemoved()
+    /**
+     * @throws InvalidDataException
+     */
+    public function testPhoneNumberValueTypeGetsRemoved(): void
     {
         $input = <<<VCF
 BEGIN:VCARD
@@ -536,6 +604,7 @@ public function testPhoneNumberValueTypeGetsRemoved()
 END:VCARD
 VCF;
 
+        /** @var VCard $vcard */
         $vcard = Reader::read($input);
         $vcard = $vcard->convert(Document::VCARD40);
 
diff --git a/tests/VObject/VersionTest.php b/tests/VObject/VersionTest.php
index 0ad9627f8..f2f240ebc 100644
--- a/tests/VObject/VersionTest.php
+++ b/tests/VObject/VersionTest.php
@@ -6,9 +6,9 @@
 
 class VersionTest extends TestCase
 {
-    public function testString()
+    public function testString(): void
     {
         $v = Version::VERSION;
-        $this->assertEquals(-1, version_compare('2.0.0', $v));
+        self::assertEquals(-1, version_compare('2.0.0', $v));
     }
 }
diff --git a/tests/VObject/WriterTest.php b/tests/VObject/WriterTest.php
index e30fac501..f5cd7a69a 100644
--- a/tests/VObject/WriterTest.php
+++ b/tests/VObject/WriterTest.php
@@ -6,29 +6,29 @@
 
 class WriterTest extends TestCase
 {
-    public function getComponent()
+    public function getComponent(): ?Document
     {
         $data = "BEGIN:VCALENDAR\r\nEND:VCALENDAR";
 
         return Reader::read($data);
     }
 
-    public function testWriteToMimeDir()
+    public function testWriteToMimeDir(): void
     {
         $result = Writer::write($this->getComponent());
-        $this->assertEquals("BEGIN:VCALENDAR\r\nEND:VCALENDAR\r\n", $result);
+        self::assertEquals("BEGIN:VCALENDAR\r\nEND:VCALENDAR\r\n", $result);
     }
 
-    public function testWriteToJson()
+    public function testWriteToJson(): void
     {
         $result = Writer::writeJson($this->getComponent());
-        $this->assertEquals('["vcalendar",[],[]]', $result);
+        self::assertEquals('["vcalendar",[],[]]', $result);
     }
 
-    public function testWriteToXml()
+    public function testWriteToXml(): void
     {
         $result = Writer::writeXml($this->getComponent());
-        $this->assertEquals(
+        self::assertEquals(
             '<?xml version="1.0" encoding="UTF-8"?>'."\n".
             '<icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">'."\n".
             ' <vcalendar/>'."\n".
diff --git a/tests/phpunit.xml b/tests/phpunit.xml
index c0588d460..01ba374c1 100644
--- a/tests/phpunit.xml
+++ b/tests/phpunit.xml
@@ -6,16 +6,21 @@
   convertWarningsToExceptions="true"
   beStrictAboutTestsThatDoNotTestAnything="true"
   beStrictAboutOutputDuringTests="true"
+  failOnRisky="true"
+  failOnWarning="true"
+  enforceTimeLimit="true"
   >
+  <php>
+    <ini name="error_reporting" value="E_ALL"/>
+  </php>
+  <coverage includeUncoveredFiles="true">
+    <include>
+      <directory suffix=".php">../lib/</directory>
+    </include>
+  </coverage>
   <testsuites>
     <testsuite name="Sabre\VObject">
       <directory>.</directory>
     </testsuite>
   </testsuites>
-
-  <filter>
-    <whitelist addUncoveredFilesFromWhitelist="true">
-        <directory suffix=".php">../lib/</directory>
-   </whitelist>
-  </filter>
 </phpunit>