The argument here is that they're confident that the bounds check isn't needed, and would prefer the compiler not insert one.
The choices therefore are:
1. No bound check
2. Bounds check inserted, but that branch isn't covered by tests
3. Bounds check inserted, and that branch is covered by tests
I'm skeptical of the claim that if (3) is infeasible then the next best option is (1)
Because if it is indeed an impossible scenario, then the lack of coverage shouldn't matter.
If it's not an impossible scenario then you have an untested case with option (1) - you've overrun the bounds of an array, which may not be a branch in the code but is definitely a different behaviour than the one you tested.
The choices therefore are:
1. No bound check
2. Bounds check inserted, but that branch isn't covered by tests
3. Bounds check inserted, and that branch is covered by tests
I'm skeptical of the claim that if (3) is infeasible then the next best option is (1)
Because if it is indeed an impossible scenario, then the lack of coverage shouldn't matter. If it's not an impossible scenario then you have an untested case with option (1) - you've overrun the bounds of an array, which may not be a branch in the code but is definitely a different behaviour than the one you tested.