I don't really like passing this to `app_run` via an ivar. I'd prefer to change `ENV` around the `assert_success` call. But on second thoughts, I don't think we need to have an acceptance test for this. If you like you could add a unit test to ensure that `Runner#env` returns `nil` in this situation, but I think the next two tests are sufficient acceptance testing for this functionality. So let's just delete this one.