Add UIKit screenshot tests for layout's Spacer

This adds the start of a new setup for hosting Kotlin tests within an iOS project so that we can use a Swift screenshot testing library. For now you have to prefix your test functions with "test" and any before/after-annotated functions need to
be named "setUp" and "tearDown" (very JUnit 3). We also do not support anything JVM-specific like rules or parameterization for now.

.github/workflows/build.yaml

@@ -74,8 +74,8 @@ jobs:
           path: build/dokka/htmlMultiModule/
           if-no-files-found: error
 
-  paparazzi:
-    runs-on: ubuntu-latest
+  screenshot-tests:
+    runs-on: macos-latest
     steps:
       - uses: actions/checkout@v4
         with:
@@ -91,6 +91,8 @@ jobs:
 
       - run: ./gradlew verifyPaparazziDebug
 
+      - run: xcodebuild -project redwood-layout-uiview/RedwoodLayoutUIViewTests.xcodeproj -scheme RedwoodLayoutUIViewTests -destination 'platform=iOS Simulator,name=iPhone 12,OS=latest' test
+
   sample-counter:
     runs-on: macos-latest
     steps:
@@ -161,9 +163,9 @@ jobs:
       - build
       - connected
       - dokka
-      - paparazzi
       - sample-counter
       - sample-emoji
+      - screenshot-tests
       - test-app
     steps:
       - uses: actions/checkout@v4

redwood-layout-shared-test/build.gradle

@@ -1,12 +1,30 @@
-apply plugin: 'org.jetbrains.kotlin.jvm'
+import app.cash.redwood.buildsupport.KmpTargets
 
-dependencies {
-  api projects.redwoodLayoutApi
-  api projects.redwoodLayoutModifiers
-  api projects.redwoodLayoutWidget
-  api projects.redwoodRuntime
-  api projects.redwoodWidget
-  api projects.redwoodYoga
-  api libs.junit
-  api libs.testParameterInjector
+apply plugin: 'org.jetbrains.kotlin.multiplatform'
+
+kotlin {
+  KmpTargets.addAllTargets(project)
+
+  sourceSets {
+    commonMain {
+      dependencies {
+        api projects.redwoodLayoutApi
+        api projects.redwoodLayoutModifiers
+        api projects.redwoodLayoutWidget
+        api projects.redwoodRuntime
+        api projects.redwoodWidget
+        api projects.redwoodYoga
+        api libs.kotlin.test
+      }
+    }
+    jvmMain {
+      dependencies {
+        // The kotlin.test library provides JVM variants for multiple testing frameworks. When used
+        // as a test dependency this selection is transparent. But since we are publishing a library
+        // we need to select one ourselves at compilation time.
+        api libs.kotlin.test.junit
+        api libs.testParameterInjector
+      }
+    }
+  }
 }

redwood-layout-shared-test/src/main/kotlin/app/cash/redwood/layout/AbstractSpacerTest.kt → redwood-layout-shared-test/src/commonMain/kotlin/app/cash/redwood/layout/AbstractSpacerTest.kt

@@ -18,7 +18,7 @@ package app.cash.redwood.layout
 import app.cash.redwood.layout.widget.Spacer
 import app.cash.redwood.ui.dp
 import app.cash.redwood.widget.Widget
-import org.junit.Test
+import kotlin.test.Test
 
 abstract class AbstractSpacerTest<T : Any> {
 
@@ -33,22 +33,22 @@ abstract class AbstractSpacerTest<T : Any> {
     height(height.dp)
   }
 
-  @Test fun zeroSpacer() {
+  @Test fun testZeroSpacer() {
     val widget = widget(width = 0, height = 0)
     verifySnapshot(wrap(widget, horizontal = true))
   }
 
-  @Test fun widthOnlySpacer() {
+  @Test fun testWidthOnlySpacer() {
     val widget = widget(width = 100, height = 0)
     verifySnapshot(wrap(widget, horizontal = true))
   }
 
-  @Test fun heightOnlySpacer() {
+  @Test fun testHeightOnlySpacer() {
     val widget = widget(width = 0, height = 100)
     verifySnapshot(wrap(widget, horizontal = false))
   }
 
-  @Test fun bothSpacer() {
+  @Test fun testBothSpacer() {
     val widget = widget(width = 100, height = 100)
     verifySnapshot(wrap(widget, horizontal = false))
   }