def test_to_dot(self):
a = []
b = []
a.append(b)
graph = ObjectGraph([a, b])
dot = graph.to_dot()
self.assertIn('{} -> {} [label="item[0]"];'.format(id(a), id(b)), dot)
self.assertIn('{} [label="list[1]"];'.format(id(a)), dot)
self.assertIn('{} [label="list[0]"];'.format(id(b)), dot)
self.assertIsInstance(dot, six.text_type)
