Use a unittest style test to support more test runners

cibuildwheel/resources/testing_temp_dir_file.py

@@ -1,9 +1,12 @@
 # this file is copied to the testing cwd, to raise the below error message if
-# pytest is run from there
+# pytest/unittest is run from there.
+
+import unittest
 
 
-def test():
+class TestStringMethods(unittest.TestCase):
-    assert False, (
+    def test_fail(self):
+        self.fail(
             "cibuildwheel executes tests from a different working directory to "
             "your project. This ensures only your wheel is imported, preventing "
             "Python from accessing files that haven't been packaged into the "

test/test_testing.py

@@ -154,7 +154,10 @@ def test_failing_test(tmp_path):
     assert len(os.listdir(output_dir)) == 0
 
 
-def test_bare_pytest_invocation(tmp_path: Path, capfd: pytest.CaptureFixture[str]):
+@pytest.mark.parametrize("test_runner", ["pytest", "unittest"])
+def test_bare_pytest_invocation(
+    tmp_path: Path, capfd: pytest.CaptureFixture[str], test_runner: str
+):
     """Check that if a user runs pytest in the the test cwd, it raises a helpful error"""
     project_dir = tmp_path / "project"
     output_dir = tmp_path / "output"
@@ -165,8 +168,10 @@ def test_bare_pytest_invocation(tmp_path: Path, capfd: pytest.CaptureFixture[str
             project_dir,
             output_dir=output_dir,
             add_env={
-                "CIBW_TEST_REQUIRES": "pytest",
+                "CIBW_TEST_REQUIRES": "pytest" if test_runner == "pytest" else "",
-                "CIBW_TEST_COMMAND": "python -m pytest",
+                "CIBW_TEST_COMMAND": (
+                    "python -m pytest" if test_runner == "pytest" else "python -m unittest"
+                ),
                 # Skip CPython 3.8 on macOS arm64, see comment above in
                 # 'test_failing_test'
                 "CIBW_SKIP": "cp38-macosx_arm64",
@@ -179,5 +184,5 @@ def test_bare_pytest_invocation(tmp_path: Path, capfd: pytest.CaptureFixture[str
 
     assert (
         "Please specify a path to your tests when invoking pytest using the {project} placeholder"
-        in captured.out
+        in captured.out + captured.err
     )