def test_extractFieldFlattenFirst(self):
        """
        L{extractField} behaves identically if the event is explicitly
        flattened first.
        """
        def flattened(evt):
            flattenEvent(evt)
            return evt
        self.test_extractField(flattened)

        L{extractField} behaves identically if the event is explicitly
        flattened first.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/logger/test/test_flatten.py