def test_size():
graph = Graph()
a = graph.add_node('a')
b = graph.add_node('b')
expected = 2
actual = graph.size()
assert actual == expected
def test_size_empty():
graph = Graph()
expected = 0
actual = graph.size()
assert actual == expected
def test_size_one():
graph = Graph()
graph.add_node("spam")
expected = 1
actual = graph.size()
assert actual == expected
def test_size_two():
graph = Graph()
graph.add_node("spam")
graph.add_node("bacon")
expected = 2
actual = graph.size()
assert actual == expected