def _runTest(self, clientProto, serverProto, clientIsServer=False):
        """
        Helper method to run TLS tests.

        @param clientProto: protocol instance attached to the client
            connection.
        @param serverProto: protocol instance attached to the server
            connection.
        @param clientIsServer: flag indicated if client should initiate
            startTLS instead of server.

        @return: a L{defer.Deferred} that will fire when both connections are
            lost.
        """
        self.clientProto = clientProto
        cf = self.clientFactory = protocol.ClientFactory()
        cf.protocol = lambda: clientProto
        if clientIsServer:
            cf.server = False
        else:
            cf.client = True

        self.serverProto = serverProto
        sf = self.serverFactory = protocol.ServerFactory()
        sf.protocol = lambda: serverProto
        if clientIsServer:
            sf.client = False
        else:
            sf.server = True

        port = reactor.listenTCP(0, sf, interface="127.0.0.1")
        self.addCleanup(port.stopListening)

        reactor.connectTCP('127.0.0.1', port.getHost().port, cf)

        return defer.gatherResults([clientProto.deferred, serverProto.deferred])

        Helper method to run TLS tests.

        @param clientProto: protocol instance attached to the client
            connection.
        @param serverProto: protocol instance attached to the server
            connection.
        @param clientIsServer: flag indicated if client should initiate
            startTLS instead of server.

        @return: a L{defer.Deferred} that will fire when both connections are
            lost.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_ssl.py