Well I would agree that undefined behaviors are unavoidable. Indeed, if you insert checks into your code to completely rule out UB, that will have a huge impact

Well I would agree that undefined behaviors are unavoidable. Indeed, if you insert checks into your code to completely rule out UB, that will have a huge impact on performance. On the other hand, I don't agree passing tests is enough. No matter how many tests you run, you can't guarantee there's no bug in your code. This is important especially when security is a critical requirement.