def test_unsupportedEncoding(self):
        """
        If an encoding unknown to the L{client.ContentDecoderAgent} is found,
        the response is unchanged.
        """
        agent = client.ContentDecoderAgent(
            self.agent, [(b'decoder1', Decoder1), (b'decoder2', Decoder2)])
        deferred = agent.request(b'GET', b'http://example.com/foo')

        req, res = self.protocol.requests.pop()

        headers = http_headers.Headers({b'foo': [b'bar'],
                                        b'content-encoding': [b'fizz']})
        response = Response((b'HTTP', 1, 1), 200, b'OK', headers, None)
        res.callback(response)

        return deferred.addCallback(self.assertIdentical, response)

        If an encoding unknown to the L{client.ContentDecoderAgent} is found,
        the response is unchanged.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_agent.py