def test_serializeAttribute(self):
        """
        The serialized form of attribute I{a} with value I{b} is C{'a="b"'}.
        """
        self.assertFlattensImmediately(tags.img(src='foo'),
                                       b'<img src="foo" />')

        The serialized form of attribute I{a} with value I{b} is C{'a="b"'}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_flatten.py