def test_illegalPASS(self):
        """
        L{pop3.POP3} handles a I{PASS} command before a I{USER} command with an
        error indicating the out-of-sequence operation.
        """
        dummy = DummyPOP3()
        client = LineSendingProtocol([
            b"PASS fooz",
            b"QUIT"
        ])
        d = loopback.loopbackAsync(dummy, client)
        return d.addCallback(self._cbTestIllegalPASS, client, dummy)

        L{pop3.POP3} handles a I{PASS} command before a I{USER} command with an
        error indicating the out-of-sequence operation.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_pop3.py