def test_formatMessage(self):
        """
        Using the message key, which is special in old-style, works for
        new-style formatting.
        """
        event = self.forwardAndVerify(
            dict(log_format="Hello, {message}!", message="world")
        )
        self.assertEqual(
            legacyLog.textFromEventDict(event),
            "Hello, world!"
        )

        Using the message key, which is special in old-style, works for
        new-style formatting.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/logger/test/test_legacy.py