def test_neighbors():
g = Graph()
g.add_edge(u"A", u"C")
g.add_edge(u"A", u"B")
g.add_edge(u"A", u"D")
g.add_edge(u"D", u"E")
assert u"B" in g.neighbors(u"A")
assert u"C" in g.neighbors(u"A")
assert u"D" in g.neighbors(u"A")
def test_neighbors_node_not_found():
g = Graph()
g.add_edge(u"A", u"C")
with pytest.raises(KeyError):
g.neighbors(u"B")
