diff --git a/test/test_infra.py b/test/test_infra.py
index be9e0da6e..4dfcbfac6 100644
--- a/test/test_infra.py
+++ b/test/test_infra.py
@@ -19,19 +19,20 @@
 import subprocess
 import sys
 import tempfile
+import typing
 import unittest
 
 import ops
 
 
-def get_python_filepaths(include_tests=True):
+def get_python_filepaths(include_tests: bool = True):
     """Helper to retrieve paths of Python files."""
     python_paths = ['setup.py']
     roots = ['ops']
     if include_tests:
         roots.append('test')
     for root in roots:
-        for dirpath, dirnames, filenames in os.walk(root):
+        for dirpath, _, filenames in os.walk(root):
             for filename in filenames:
                 if filename.endswith(".py"):
                     python_paths.append(os.path.join(dirpath, filename))
@@ -42,7 +43,7 @@ class InfrastructureTests(unittest.TestCase):
 
     def test_quote_backslashes(self):
         # ensure we're not using unneeded backslash to escape strings
-        issues = []
+        issues : typing.List[typing.Tuple[str, int, str]] = []
         for filepath in get_python_filepaths():
             with open(filepath, "rt", encoding="utf8") as fh:
                 for idx, line in enumerate(fh, 1):
@@ -54,7 +55,7 @@ def test_quote_backslashes(self):
 
     def test_ensure_copyright(self):
         # all non-empty Python files must have a proper copyright somewhere in the first 5 lines
-        issues = []
+        issues : typing.List[str] = []
         regex = re.compile(r"# Copyright \d\d\d\d(-\d\d\d\d)? Canonical Ltd.\n")
         for filepath in get_python_filepaths():
             if os.stat(filepath).st_size == 0:
@@ -69,7 +70,7 @@ def test_ensure_copyright(self):
         if issues:
             self.fail("Please add copyright headers to the following files:\n" + "\n".join(issues))
 
-    def _run_setup(self, *args):
+    def _run_setup(self, *args: str) -> str:
         proc = subprocess.run(
             (sys.executable, 'setup.py') + args,
             stdout=subprocess.PIPE,
@@ -101,7 +102,7 @@ def test_install_requires(self):
 
         # For some reason "setup.py --requires" doesn't work, so do this the hard way
         with open('setup.py', encoding='utf-8') as f:
-            lines = []
+            lines : typing.List[str] = []
             for line in f:
                 if 'install_requires=[' in line:
                     break
@@ -131,7 +132,7 @@ def test_imports(self):
             with self.subTest(name=name):
                 self.check(name)
 
-    def check(self, name):
+    def check(self, name : str):
         """Helper function to run the test."""
         fd, testfile = tempfile.mkstemp()
         self.addCleanup(os.unlink, testfile)