def test_sourceOnClass(self):
        """
        C{log_source} event key refers to the class.
        """
        def observer(event):
            self.assertEqual(event["log_source"], Thingo)

        class Thingo(object):
            log = TestLogger(observer=observer)

        Thingo.log.info()

        C{log_source} event key refers to the class.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/logger/test/test_logger.py