def test_get_neighbors_none():
g = Graph()
node_a = g.add_node('a')
node_b = g.add_node('b')
node_c = g.add_node('c')
node_d = g.add_node('d')
actual = g.get_neighbors(node_a)
expected = []
assert actual == expected
def test_get_neighbors_1():
g = Graph()
node_a = g.add_node('a')
node_b = g.add_node('b')
node_c = g.add_node('c')
node_d = g.add_node('d')
g.add_edge(node_a, node_b)
actual = len(g.get_neighbors(node_a))
expected = 1
assert actual == expected