def test_opt_charsetMissingIdentifier(self):
        """
        A line that contains C{CHARSET} but no character set
        identifier raises L{imap4.IllegalClientResponse}.
        """
        line = b"CHARSET"
        self.assertRaises(imap4.IllegalClientResponse,
                          self.server.opt_charset, line)

        A line that contains C{CHARSET} but no character set
        identifier raises L{imap4.IllegalClientResponse}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_imap.py