def test_add_edge():
g = Graph()
g.add_node(1)
g.add_edge(3, 2)
assert len(g.nodes()) == 3
assert ({3, 2}, 1) in g.edges()
def test_add_vertex():
g = Graph()
g.add_node(1)
g.add_node(2)
assert 1 in g.nodes()
assert 2 in g.nodes()