def test_helloWorld(self):
        """
        Verify that a simple command can be sent and its response received with
        the simple low-level string-based API.
        """
        c, s, p = connectedServerAndClient()
        L = []
        HELLO = b'world'
        c.sendHello(HELLO).addCallback(L.append)
        p.flush()
        self.assertEqual(L[0][b'hello'], HELLO)

        Verify that a simple command can be sent and its response received with
        the simple low-level string-based API.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_amp.py