def test_start_is_stop():
g = DirectedGraph()
g.add_edge('a', 'b')
g.add_edge('b', 'c')
g.add_edge('b', 'd')
g.add_edge('e', 'f')
assert depth_first_search(g, 'a', 'a') == ['a']
def test_single_path_directed():
g = DirectedGraph()
g.add_edge('a', 'b')
g.add_edge('b', 'c')
g.add_edge('b', 'd')
g.add_edge('d', 'e')
g.add_edge('e', 'f')
assert depth_first_search(g, 'a', 'e') == ['a', 'b', 'd', 'e']
def test_no_path_undirected():
'''
Test BFS on a simple undirected graph that contains a no cycles, and no path to the goal.
'''
g = UndirectedGraph()
g.add_edge('a', 'b')
g.add_edge('b', 'c')
g.add_edge('b', 'd')
g.add_edge('e', 'f')
assert depth_first_search(g, 'a', 'e') is None
def test_multiple_paths_directed():
g = DirectedGraph()
g.add_edge('a', 'b')
g.add_edge('b', 'c')
g.add_edge('b', 'e')
g.add_edge('b', 'd')
g.add_edge('d', 'e')
g.add_edge('e', 'f')
found_path = depth_first_search(g, 'a', 'e')
assert found_path == ['a', 'b', 'e'] or found_path == ['a', 'b', 'd', 'e']
def test_no_path_directed_cycles():
'''
Test BFS on a simple directed graph that contains cycles, but no path to the goal.
'''
g = DirectedGraph()
g.add_edge('a', 'b')
g.add_edge('b', 'c')
g.add_edge('c', 'a')
g.add_edge('b', 'd')
g.add_edge('e', 'f')
assert depth_first_search(g, 'a', 'e') is None
def test_single_path_with_cycles_directed():
g = DirectedGraph()
g.add_edge('a', 'b')
g.add_edge('b', 'c')
g.add_edge('c', 'h')
g.add_edge('h', 'i')
g.add_edge('i', 'j')
g.add_edge('j', 'k')
g.add_edge('b', 'd')
g.add_edge('d', 'e')
g.add_edge('e', 'f')
g.add_edge('f', 'b')
assert depth_first_search(g, 'a',
'k') == ['a', 'b', 'c', 'h', 'i', 'j', 'k']