def test_ensure_not_cyclic__raises(self):
dag = DepDag()
dag.a.depends_on('b')
dag.b.depends_on('a')
with self.assertRaisesRegex(CycleDetected, 'graph is cyclic'):
dag.ensure_not_cyclic()
def test_ensure_not_cyclic__passes(self):
dag = DepDag()
dag.a.depends_on('b')
dag.b.depends_on('c', 'd')
dag.ensure_not_cyclic()
