def test_emptyLine(self):
        """
        L{imap4.IMAP4Server.parse_command} sends a C{BAD} response to
        an empty line.
        """
        self.server.parse_command(b"")

        self.assertEqual(self.transport.value(), b"* BAD Null command\r\n")

        L{imap4.IMAP4Server.parse_command} sends a C{BAD} response to
        an empty line.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_imap.py