def test_badSubsystemDoesNotCreateClient(self):
        """
        When a subsystem request fails, SSHSession.client should not be set.
        """
        ret = self.session.requestReceived(
            b'subsystem', common.NS(b'BadSubsystem'))
        self.assertFalse(ret)
        self.assertIsNone(self.session.client)

        When a subsystem request fails, SSHSession.client should not be set.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_session.py