def test_find_shortest_chain_returns_none_if_not_exists():
graph = ImportGraph()
a, b, c = "foo", "bar", "baz"
graph.add_import(importer=a, imported=b)
graph.add_import(importer=b, imported=c)
assert None is graph.find_shortest_chain(importer=c, imported=a)
def test_find_shortest_chain_when_exists():
graph = ImportGraph()
a, b, c = "foo", "bar", "baz"
d, e, f = "long", "way", "around"
# Add short path.
graph.add_import(importer=a, imported=b)
graph.add_import(importer=b, imported=c)
# Add longer path.
graph.add_import(importer=a, imported=d)
graph.add_import(importer=d, imported=e)
graph.add_import(importer=e, imported=f)
graph.add_import(importer=f, imported=c)
assert (a, b, c) == graph.find_shortest_chain(importer=a, imported=c)