def METHOD_NAME(self):
    with self.assertRaises(ValidationError):
        EnsureDirsExistItem(
            from_target="t",
            into_dir="a/b",
            basename="c",
            subdirs_to_create="b/c",
        )
    # don't even allow None
    with self.assertRaises(ValidationError):
        EnsureDirsExistItem(
            from_target="t",
            into_dir="a/b",
            basename="c",
            subdirs_to_create=None,
        )