def test_success(self):
        """
        L{client.readBody} returns a L{Deferred} which fires with the complete
        body of the L{IResponse} provider passed to it.
        """
        response = DummyResponse()
        d = client.readBody(response)
        response.protocol.dataReceived(b"first")
        response.protocol.dataReceived(b"second")
        response.protocol.connectionLost(Failure(ResponseDone()))
        self.assertEqual(self.successResultOf(d), b"firstsecond")

        L{client.readBody} returns a L{Deferred} which fires with the complete
        body of the L{IResponse} provider passed to it.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_agent.py