def test_saveUnPersistable(self):
        """
        Saving and loading an object which cannot be represented in JSON will
        result in a placeholder.
        """
        self.assertEqual(
            eventFromJSON(self.savedEventJSON({u"1": 2, u"3": object()})),
            {u"1": 2, u"3": {u"unpersistable": True}}
        )

        Saving and loading an object which cannot be represented in JSON will
        result in a placeholder.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/logger/test/test_json.py