def test_to_json(self):
# XXX Needs a better test. For now, just exercise the
# to_json method.
a = []
b = []
a.append(b)
graph = ObjectGraph([a, b])
json_graph = graph.to_json()
self.assertIsInstance(json_graph, six.text_type)
# Make sure that the result is valid json.
json.loads(json_graph)
