def test_createWithSingleWildcard(self):
        """
        Creating a L{MessageSet} with a single L{None}, representing
        C{*}, adds C{*} to the range; its serialized form includes
        only C{*}, its length is one, but it cannot be iterated over
        because its endpoint is unknown.
        """
        m = MessageSet(None)
        self.assertEqual(str(m), "*")
        self.assertEqual(len(m), 1)
        self.assertRaises(TypeError, list, m)

        Creating a L{MessageSet} with a single L{None}, representing
        C{*}, adds C{*} to the range; its serialized form includes
        only C{*}, its length is one, but it cannot be iterated over
        because its endpoint is unknown.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_imap.py