def getConnectedClientAndServer(self, reactor, interface, addressFamily):
        """
        Return a L{Deferred} firing with a L{MyClientFactory} and
        L{MyServerFactory} connected pair, and the listening C{Port}. The
        particularity is that the server protocol has been obtained after doing
        a C{adoptStreamConnection} against the original server connection.
        """
        firstServer = MyServerFactory()
        firstServer.protocolConnectionMade = Deferred()

        server = MyServerFactory()
        server.protocolConnectionMade = Deferred()
        server.protocolConnectionLost = Deferred()

        client = MyClientFactory()
        client.protocolConnectionMade = Deferred()
        client.protocolConnectionLost = Deferred()

        # self.mktemp() often returns a path which is too long to be used.
        path = mktemp(suffix='.sock', dir='.')
        port = reactor.listenUNIX(path, firstServer)

        def firstServerConnected(proto):
            reactor.removeReader(proto.transport)
            reactor.removeWriter(proto.transport)
            reactor.adoptStreamConnection(
                proto.transport.fileno(), AF_UNIX, server)

        firstServer.protocolConnectionMade.addCallback(firstServerConnected)

        lostDeferred = gatherResults([client.protocolConnectionLost,
                                      server.protocolConnectionLost])
        def stop(result):
            if reactor.running:
                reactor.stop()
            return result

        lostDeferred.addBoth(stop)

        deferred = Deferred()
        deferred.addErrback(stop)

        startDeferred = gatherResults([client.protocolConnectionMade,
                                       server.protocolConnectionMade])
        def start(protocols):
            client, server = protocols
            deferred.callback((client, server, port))

        startDeferred.addCallback(start)

        reactor.connectUNIX(port.getHost().name, client)
        return deferred

        Return a L{Deferred} firing with a L{MyClientFactory} and
        L{MyServerFactory} connected pair, and the listening C{Port}. The
        particularity is that the server protocol has been obtained after doing
        a C{adoptStreamConnection} against the original server connection.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_unix.py