def test_undirected_neighbors():
# given
g = UndirectedGraph()
# when
g.add_edge(1, 3)
g.add_edge(3, 1)
g.add_edge(5, 1)
g.add_edge(1, 6)
# then
assert set(g.neighbors(1)) == {3, 5, 6}
assert set(g.neighbors(6)) == {1}
def test_add_node_already_graph_does_nothing():
# given
g = UndirectedGraph()
# when
g.add_edge(1, 3)
g.add_edge(3, 1)
g.add_edge(5, 1)
g.add_node(3)
assert len(g.neighbors(3)) == 1
assert len(g.nodes) == 3