def test_collect_invalid_signature_message(pytester: Pytester) -> None:
    """Check that we issue a proper message when we can't determine the signature of a test
    function (#4026).
    """
    pytester.makepyfile(
        """
        import pytest

        class TestCase:
            @pytest.fixture
            def fix():
                pass
    """
    )
    result = pytester.runpytest()
    result.stdout.fnmatch_lines(
        ["Could not determine arguments of *.fix *: invalid method signature"]
    )
Check that we issue a proper message when we can't determine the signature of a test
    function (#4026).
    
testing/test_collection.py