That's a solid plan for acceptance testing and a great way to make sure you can never test diagnostic, recovery, rollback, and other something-abnormal-happened

That's a solid plan for acceptance testing and a great way to make sure you can never test diagnostic, recovery, rollback, and other something-abnormal-happened-here logic. For small programs with few interfaces to worry about, that might be fine, but as you number of users go up, the odds go up that you'll be ensuring rollback bits get flipped when filesystems fail. None of that is simple to test without some sort of dependency injection or other heavyweight design pattern.