def test_unexpectedEOF(self):
        """
        Unexpected disconnects get converted to ConnectionLost errors.
        """
        tlsClient, tlsServer, handshakeDeferred, disconnectDeferred = (
            self.handshakeProtocols())
        serverProtocol = tlsServer.wrappedProtocol
        data = []
        reason = []
        serverProtocol.dataReceived = data.append
        serverProtocol.connectionLost = reason.append

        # Write data, then disconnect *underlying* transport, resulting in an
        # unexpected TLS disconnect:
        def handshakeDone(ign):
            tlsClient.write(b"hello")
            tlsClient.transport.loseConnection()
        handshakeDeferred.addCallback(handshakeDone)

        # Receiver should be disconnected, with ConnectionLost notification
        # (masking the Unexpected EOF SSL error):
        def disconnected(ign):
            self.assertTrue(reason[0].check(ConnectionLost), reason[0])
        disconnectDeferred.addCallback(disconnected)
        return disconnectDeferred

        Unexpected disconnects get converted to ConnectionLost errors.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/protocols/test/test_tls.py