def METHOD_NAME():
    """
    make sure the files didn't get rewritten, because nothing changed:
    """
    before = list(map(os.path.getmtime, files))
    # introduce a small delay, to make the test valid
    test.sleep()
    # should still be up-to-date
    test.up_to_date(arguments='.')
    after = list(map(os.path.getmtime, files))
    test.fail_test(before != after)