def test_interface(self):
        """
        A L{FileLogObserver} returned by L{jsonFileLogObserver} is an
        L{ILogObserver}.
        """
        with StringIO() as fileHandle:
            observer = jsonFileLogObserver(fileHandle)
            try:
                verifyObject(ILogObserver, observer)
            except BrokenMethodImplementation as e:
                self.fail(e)

        A L{FileLogObserver} returned by L{jsonFileLogObserver} is an
        L{ILogObserver}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/logger/test/test_json.py