def test_modules_not_importable_as_side_effect(self, pytester: Pytester) -> None:
        """In import-mode `importlib`, modules in folders containing conftest.py are not
        importable, as don't change sys.path or sys.modules as side effect of importing
        the conftest.py file.
        """
        self.setup_conftest_and_foo(pytester)
        result = pytester.runpytest("-v", "--import-mode=importlib")
        result.stdout.fnmatch_lines(
            [
                "*ModuleNotFoundError: No module named 'foo'",
                "tests?test_foo.py:2: ModuleNotFoundError",
                "* 1 failed in *",
            ]
        )
In import-mode `importlib`, modules in folders containing conftest.py are not
        importable, as don't change sys.path or sys.modules as side effect of importing
        the conftest.py file.
        
testing/test_collection.py