def test_unmarkedObserversDeprecated(self):
        """
        L{app.AppLogger} using a logger observer which does not implement
        L{ILogObserver} or L{LegacyILogObserver} will be wrapped in a compat
        shim and raise a L{DeprecationWarning}.
        """
        logs = []
        logger = app.AppLogger({})
        logger._getLogObserver = lambda: logs.append
        logger.start(Componentized())

        self.assertIn("starting up", textFromEventDict(logs[0]))

        warnings = self.flushWarnings(
            [self.test_unmarkedObserversDeprecated])
        self.assertEqual(len(warnings), 1)
        self.assertEqual(warnings[0]["message"],
                         ("Passing a logger factory which makes log observers "
                          "which do not implement twisted.logger.ILogObserver "
                          "or twisted.python.log.ILogObserver to "
                          "twisted.application.app.AppLogger was deprecated "
                          "in Twisted 16.2. Please use a factory that "
                          "produces twisted.logger.ILogObserver (or the "
                          "legacy twisted.python.log.ILogObserver) "
                          "implementing objects instead."))

        L{app.AppLogger} using a logger observer which does not implement
        L{ILogObserver} or L{LegacyILogObserver} will be wrapped in a compat
        shim and raise a L{DeprecationWarning}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_twistd.py