def METHOD_NAME(self):
    builder = self.builder_for_features()
    # Since the builder advertises no features, you can't find it
    # by looking up features.
    self.assertEqual(self.registry.lookup('foo'), None)
    # But you can find it by doing a lookup with no features, if
    # this happens to be the only registered builder.
    self.assertEqual(self.registry.lookup(), builder)