test_graph.py 文件源码

def test_has_cycle_implicit():
    """A Vertex is accessible to the Graph but not explicitly part of it."""
    a = Vertex(Vertex._make_test_vertex())
    b = Vertex(Vertex._make_test_vertex())
    c = Vertex(Vertex._make_test_vertex())
    a.add_edge(Edge(b))
    b.add_edge(Edge(c))
    c.add_edge(Edge(a))
    g = Graph([a, b])
    assert g.has_cycle()