def test_add_edge_nodes():
'''
Adding an edge between non-existant edges should cause those nodes to be
returned by .nodes().
'''
g = UndirectedGraph()
assert g.add_edge('a', 'b', 42)
assert len(list(g.nodes())) == 2
assert 'a' in g.nodes()
assert 'b' in g.nodes()
def test_add_nodes():
'''
Adding a node should cause that node to appear in the return value of .nodes().
'''
g = UndirectedGraph()
assert g.add_node('a')
assert 'a' in g.nodes()
assert len(list(g.nodes())) == 1
assert g.add_node('a') == False
assert 'a' in g.nodes()
assert len(list(g.nodes())) == 1
assert g.add_node('b')
assert 'a' in g.nodes()
assert 'b' in g.nodes()
assert len(list(g.nodes())) == 2
def test_simple_integration():
'''
test a simple use case, retesting assumptions at each step.
'''
g = UndirectedGraph()
assert g.add_node('a')
assert g.contains('a')
assert len(list(g.nodes())) == 1
assert 'a' in g.nodes()
assert len(list(g.neighbors('a'))) == 0
assert g.add_node('b')
assert g.contains('b')
assert len(list(g.nodes())) == 2
assert 'a' in g.nodes()
assert 'b' in g.nodes()
assert len(list(g.neighbors('a'))) == 0
assert len(list(g.neighbors('b'))) == 0
assert g.add_node('c')
assert g.contains('c')
assert len(list(g.nodes())) == 3
assert 'a' in g.nodes()
assert 'b' in g.nodes()
assert 'c' in g.nodes()
assert len(list(g.neighbors('a'))) == 0
assert len(list(g.neighbors('b'))) == 0
assert len(list(g.neighbors('c'))) == 0
g.add_edge('a', 'b')
edges = list(g.edges())
assert len(edges) == 2
assert ('a', 'b', 1) in edges
assert ('b', 'a', 1) in edges
assert g.contains('a')
assert g.contains('b')
assert g.contains('c')
assert len(list(g.nodes())) == 3
assert 'a' in g.nodes()
assert 'b' in g.nodes()
assert 'c' in g.nodes()
assert len(list(g.neighbors('a'))) == 1
assert ('b', 1) in g.neighbors('a')
assert len(list(g.neighbors('b'))) == 1
assert ('a', 1) in g.neighbors('b')
assert len(list(g.neighbors('c'))) == 0
g.add_edge('a', 'c')
edges = list(g.edges())
assert len(edges) == 4
assert ('a', 'b', 1) in edges
assert ('b', 'a', 1) in edges
assert ('a', 'c', 1) in edges
assert ('c', 'a', 1) in edges
assert g.contains('a')
assert g.contains('b')
assert g.contains('c')
assert len(list(g.nodes())) == 3
assert 'a' in g.nodes()
assert 'b' in g.nodes()
assert 'c' in g.nodes()
assert len(list(g.neighbors('a'))) == 2
assert ('b', 1) in g.neighbors('a')
assert ('c', 1) in g.neighbors('a')
assert len(list(g.neighbors('b'))) == 1
assert ('a', 1) in g.neighbors('b')
assert len(list(g.neighbors('c'))) == 1
assert ('a', 1) in g.neighbors('c')
edges = list(g.edges())
assert ('a', 'b', 1) in edges
assert ('b', 'a', 1) in edges
assert ('a', 'c', 1) in edges
assert ('c', 'a', 1) in edges