def test_ancestors(self):
a = []
b = []
c = []
d = []
a.append(b)
a.append(c)
b.append(d)
c.append(d)
graph = ObjectGraph([a, b, c, d])
self.assertCountEqual(graph.ancestors(a), [a])
self.assertCountEqual(graph.ancestors(b), [b, a])
self.assertCountEqual(graph.ancestors(c), [c, a])
self.assertCountEqual(graph.ancestors(d), [d, b, c, a])