def test_exchange(self):
        """
        Test that a datagram can be sent to and received by a server and vice
        versa.
        """
        clientaddr = self.mktemp()
        serveraddr = self.mktemp()
        sp = ServerProto()
        cp = ClientProto()
        s = reactor.listenUNIXDatagram(serveraddr, sp)
        self.addCleanup(s.stopListening)
        c = reactor.connectUNIXDatagram(serveraddr, cp, bindAddress=clientaddr)
        self.addCleanup(c.stopListening)

        d = defer.gatherResults([sp.deferredStarted, cp.deferredStarted])
        def write(ignored):
            cp.transport.write(b"hi")
            return defer.gatherResults([sp.deferredGotWhat,
                                        cp.deferredGotBack])

        def _cbTestExchange(ignored):
            self.assertEqual(b"hi", sp.gotwhat)
            self.assertEqual(clientaddr, sp.gotfrom)
            self.assertEqual(b"hi back", cp.gotback)

        d.addCallback(write)
        d.addCallback(_cbTestExchange)
        return d

        Test that a datagram can be sent to and received by a server and vice
        versa.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_unix.py