The other problem is that finding tests that cover everything from the public interfaces can be extremely difficult. Most test suites don't achieve full coverage even of theoretically reachable points in the code.
If they aren't then you are defending against situations that can never occur. In that case the check seems unnecessary, and I at least wouldn't make it a priority to cover it. Also, those checks are usually simple enough that one can reason about them easily, again making it less of a priority to have tests cover them.
> The other problem is that finding tests that cover everything from the public interfaces can be extremely difficult. Most test suites don't achieve full coverage even of theoretically reachable points in the code.
Yes, testing is hard. That is not a reason to write more detrimental tests though.
This insight of yours cannot help but save on costs. Be sure to suggest it to management.
Do you have any particular example in mind that is not superfluous and really can not be exercised by the public API? I have a hard time thinking of any.
Sounds like a good idea, actually. These places being the entire surface of your code that is exposed to the real world. So not unlike what I have been suggesting.