Run mypy in GitHub CI

Author: jelmer

.github/workflows/test.yml

@@ -44,6 +44,10 @@ jobs:
         run: |
           python -m ruff format --check .
 
+      - name: Type Check
+        run: |
+          python -m mypy testtools
+
       - name: Tests
         run: |
           python -W once -m testtools.run testtools.tests.test_suite

pyproject.toml

@@ -34,7 +34,7 @@ Homepage = "https://github.com/testing-cabal/testtools"
 [project.optional-dependencies]
 test = ["testscenarios", "testresources"]
 twisted = ["Twisted", "fixtures"]
-dev = ["ruff==0.12.3"]
+dev = ["ruff==0.12.3", "mypy>=1.0.0"]
 
 [tool.hatch.version]
 source = "vcs"

testtools/tests/twistedsupport/_helpers.py

@@ -10,6 +10,7 @@
 
 if TYPE_CHECKING:
     from types import ModuleType
+
     defer: Optional[ModuleType]
 else:
     try: