def METHOD_NAME(self):
    self.registry.register('MyCustomTransformerNeedsY',
                           'custom_transformer.CustomTransformerNeedsY',
                           'Transformer')
    with self.assertRaises(ValueError):
        self.registry.register('MyCustomTransformerNeedsYWrongInterface',
                               'custom_transformer.CustomTransformerNeedsYWrongInterface',
                               'Transformer')