def test_proxyAttribute(self):
        """
        Proxy objects should proxy declared attributes, but not other
        attributes.
        """
        yayable = Yayable()
        yayable.ifaceAttribute = object()
        proxy = proxyForInterface(IProxiedInterface)(yayable)
        self.assertIs(proxy.ifaceAttribute, yayable.ifaceAttribute)
        self.assertRaises(AttributeError, lambda: proxy.yays)

        Proxy objects should proxy declared attributes, but not other
        attributes.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_components.py