def cbClientStarted(ignored):
            """
            Send a datagram from the client once it's started.

            @param ignored: a list of C{[None, None]}, which is ignored
            @returns: a deferred which fires when the server has received a
                datagram.
            """

            client.transport.connect("::1", server.transport.getHost().port)
            client.transport.write(b"spam")
            serverReceived = server.packetReceived = defer.Deferred()
            return serverReceived

            Send a datagram from the client once it's started.

            @param ignored: a list of C{[None, None]}, which is ignored
            @returns: a deferred which fires when the server has received a
                datagram.
            
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_udp.py