def remote_unknownError(self):
        """
        Fail with error that is not known to client.
        """
        class UnknownError(pb.Error):
            pass
        raise UnknownError("I'm not known to client!")

        Fail with error that is not known to client.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/spread/test/test_pbfailure.py