def test_dictionary(self):
        """
        Test references search through a dictionary, as a key or as a value.
        """
        o = object()
        d1 = {None: o}
        d2 = {o: None}

        self.assertIn("[None]", reflect.objgrep(d1, o, reflect.isSame))
        self.assertIn("{None}", reflect.objgrep(d2, o, reflect.isSame))

        Test references search through a dictionary, as a key or as a value.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_reflect.py