def test_isError(self):
        """
        If C{"isError"} is set to C{1} (true) on the legacy event, the
        C{"log_level"} key should get set to L{LogLevel.critical}.
        """
        publishToNewObserver(
            self.observer,
            self.legacyEvent(isError=1),
            legacyLog.textFromEventDict
        )
        self.assertEqual(self.events[0]["log_level"], LogLevel.critical)

        If C{"isError"} is set to C{1} (true) on the legacy event, the
        C{"log_level"} key should get set to L{LogLevel.critical}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/logger/test/test_legacy.py