def test_remove_edge(self):
g = Graph()
vertex1 = g.add_vertex('v1')
vertex2 = g.add_vertex('v2')
vertex3 = g.add_vertex('v3')
edge1 = g.add_edge(vertex1, vertex2)
edge2 = g.add_edge(vertex2, vertex3)
g.remove_edge(edge1)
self.assertEqual(1, len(g.edges))
self.assertTrue(edge1 not in g.edges)
self.assertTrue(vertex2 not in vertex1.neighbors)
g.remove_edge_between('v2', vertex3)
self.assertEqual(0, len(g.edges))
self.assertTrue(edge2 not in g.edges)
self.assertTrue(vertex3 not in vertex2.neighbors)
