def assertFailure(self, deferred, exception):
        return assert_fails_with(deferred, exception)
utility function to check if borg can open a repository
dataset/ETHPy150Open ClusterHQ/flocker/flocker/testtools/_base.py/AsyncTestCase.assertFailure--crossover with--dataset/ETHPy150Open borgbackup/borg/borg/testsuite/upgrader.py/repo_valid