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])