def test_has_node():
g = Graph()
assert g.has_node('a') is False
g.add_node('a')
assert g.has_node('a') is True
g.add_edge('b', 'c')
assert g.has_node('b') is True
g.del_edge('b', 'c')
assert g.has_node('c') is True
def test_delete_node():
g = Graph()
try:
g.delete_node('a')
except IndexError:
assert True
else:
assert False
for letter in ['a', 'b', 'c', 'd']:
g.add_node(letter)
g.add_edge('a', 'b')
g.add_edge('b', 'c')
g.add_edge('a', 'c')
g.add_edge('b', 'd')
g.delete_node('d')
for edge in g._edges:
assert 'd' not in edge.connects
assert len(g._edges) == 3
g.delete_node('a')
assert len(g._edges) == 1
for edge in g._edges:
assert edge.connects == {'b', 'c'}
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()