def test_unixCheckerSucceeds(self):
        """
        The checker works with valid credentials.
        """
        def _gotAvatar(username):
            self.assertEqual(username, self.admin.username)
        return (self.checker
                .requestAvatarId(self.admin)
                .addCallback(_gotAvatar))

        The checker works with valid credentials.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/cred/test/test_strcred.py