Use a unittest style test to support more test runners

cibuildwheel/resources/testing_temp_dir_file.py

@@ -1,14 +1,17 @@
 # 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():
-    assert False, (
-        "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 "
-        "wheel. Please specify a path to your tests when invoking pytest "
-        "using the {project} placeholder, e.g. `pytest {project}` or "
-        "`pytest {project}/tests`. cibuildwheel will replace {project} with "
-        "the path to your project."
-    )
+class TestStringMethods(unittest.TestCase):
+    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 "
+            "wheel. Please specify a path to your tests when invoking pytest "
+            "using the {project} placeholder, e.g. `pytest {project}` or "
+            "`pytest {project}/tests`. cibuildwheel will replace {project} with "
+            "the path to your project."
+        )