def METHOD_NAME(self) -> None:
    """
    If the challenge just has a rspauth directive, the response is empty.
    """
    challenge = b"rspauth=cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZA=="
    response = self.mechanism.getResponse(challenge)
    self.assertEqual(b"", response)