def run(self):
        """
        A fake run method, checking that it's been called one and only time.
        """
        if self.called:
            raise RuntimeError("Already called")
        self.called = True

        A fake run method, checking that it's been called one and only time.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_twistd.py