def test_applicationDataBeforeCommand(self):
        """
        Application bytes received before a WILL/WONT/DO/DONT are delivered
        before the command is processed.
        """
        self.protocol.commandMap = {}
        self._deliver(
            b'y' + telnet.IAC + telnet.WILL + b'\x00',
            ('bytes', b'y'), ('command', telnet.WILL, b'\x00'))

        Application bytes received before a WILL/WONT/DO/DONT are delivered
        before the command is processed.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_telnet.py