def test_client_extReceivedWithoutWriteErr(self):
        """
        SSHSession.extReceived() should handle the case where the transport
        on the client doesn't have a writeErr method.
        """
        client = self.session.client = StubClient()
        client.transport = StubTransport() # doesn't have writeErr

        # should not raise an error
        self.session.extReceived(connection.EXTENDED_DATA_STDERR, b'ignored')

        SSHSession.extReceived() should handle the case where the transport
        on the client doesn't have a writeErr method.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_session.py