def link_user(self, request, user, **kwargs):
        raise NotImplementedError('This method must be set by a subclass.')
ensure that a class attribute can be overriden by kwarg. Also
dataset/ETHPy150Open bryanveloso/hello-social-registration/social_registration/backends/default/__init__.py/DefaultBackend.link_user--crossover with--dataset/ETHPy150Open icook/yota/src/yota/tests/test_nodes.py/TestNode.test_class_override