def test_bellman_ford_negative():
"""Bellman Ford algorithm test with negative cycle"""
graph = SimpleGraph([('a', 'b', -1), ('b', 'a', -3), ('a', 'g', 1),
('g', 'b', 1)])
assert graph.bellmanford('a') == 'Graph contains a negative-weight cycle'
def test_bellman_ford():
"""basic Bellman Ford algorithm test"""
graph = SimpleGraph([('a', 'b', 6), ('b', 'a', 5), ('a', 'g', 1),
('g', 'b', 1)])
assert graph.bellmanford('a') == {'a': 0, 'b': 2, 'g': 1}