def test_serializeDeferredSlots(self):
        """
        Test that a slot with a deferred as its value will be flattened using
        the value from the deferred.
        """
        t = tags.p(slot('test'))
        t.fillSlots(test=succeed(tags.em('four>')))
        return self.assertFlattensTo(t, b'<p><em>four&gt;</em></p>')

        Test that a slot with a deferred as its value will be flattened using
        the value from the deferred.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_flatten.py