def test_predecessors(self):
g = DiGraph()
g.add_edge("foo", "bar")
g.add_edge("foo", "baz")
g.add_node("qux")
self.assertIn("foo", list(g.predecessors("bar")))
self.assertIn("foo", list(g.predecessors("baz")))
self.assertEqual(len(list(g.predecessors("qux"))), 0)
def test_predecessor_not_in_graph(self):
g = DiGraph()
with self.assertRaises(ValueError):
g.predecessors("not in graph")