def test_disconnectAfterWriteAfterStartTLS(self):
        """
        L{ITCPTransport.loseConnection} ends a connection which was set up with
        L{ITLSTransport.startTLS} and which has recently been written to.  This
        is intended to verify that a socket send error masked by the TLS
        implementation doesn't prevent the connection from being reported as
        closed.
        """
        class ShortProtocol(Protocol):
            def connectionMade(self):
                if not ITLSTransport.providedBy(self.transport):
                    # Functionality isn't available to be tested.
                    finished = self.factory.finished
                    self.factory.finished = None
                    finished.errback(SkipTest("No ITLSTransport support"))
                    return

                # Switch the transport to TLS.
                self.transport.startTLS(self.factory.context)
                # Force TLS to really get negotiated.  If nobody talks, nothing
                # will happen.
                self.transport.write(b"x")

            def dataReceived(self, data):
                # Stuff some bytes into the socket.  This mostly has the effect
                # of causing the next write to fail with ENOTCONN or EPIPE.
                # With the pyOpenSSL implementation of ITLSTransport, the error
                # is swallowed outside of the control of Twisted.
                self.transport.write(b"y")
                # Now close the connection, which requires a TLS close alert to
                # be sent.
                self.transport.loseConnection()

            def connectionLost(self, reason):
                # This is the success case.  The client and the server want to
                # get here.
                finished = self.factory.finished
                if finished is not None:
                    self.factory.finished = None
                    finished.callback(reason)

        reactor = self.buildReactor()

        serverFactory = ServerFactory()
        serverFactory.finished = Deferred()
        serverFactory.protocol = ShortProtocol
        serverFactory.context = self.getServerContext()

        clientFactory = ClientFactory()
        clientFactory.finished = Deferred()
        clientFactory.protocol = ShortProtocol
        clientFactory.context = self.getClientContext()
        clientFactory.context.method = serverFactory.context.method

        lostConnectionResults = []
        finished = DeferredList(
            [serverFactory.finished, clientFactory.finished],
            consumeErrors=True)
        def cbFinished(results):
            lostConnectionResults.extend([results[0][1], results[1][1]])
        finished.addCallback(cbFinished)

        port = reactor.listenTCP(0, serverFactory, interface='127.0.0.1')
        self.addCleanup(port.stopListening)

        connector = reactor.connectTCP(
            port.getHost().host, port.getHost().port, clientFactory)
        self.addCleanup(connector.disconnect)

        finished.addCallback(lambda ign: reactor.stop())
        self.runReactor(reactor)
        lostConnectionResults[0].trap(ConnectionClosed)
        lostConnectionResults[1].trap(ConnectionClosed)

        L{ITCPTransport.loseConnection} ends a connection which was set up with
        L{ITLSTransport.startTLS} and which has recently been written to.  This
        is intended to verify that a socket send error masked by the TLS
        implementation doesn't prevent the connection from being reported as
        closed.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_tls.py