def test_add_contains():
'''
Adding a node should cause contains to return true, adding a duplicate
should return False, and contains should still report True for that node
'''
g = UndirectedGraph()
assert g.add_node('a')
assert g.contains('a')
assert g.add_node('a') == False
assert g.contains('a')
def test_add_edge_contains():
'''
Adding an edge between non-existant edges should cause contains to report they
exist.
'''
g = UndirectedGraph()
assert g.add_edge('a', 'b', 42)
assert g.contains('a')
assert g.contains('b')
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