[MattPalmer1086]

Yep, nothing gives you complete assurance of correctness. Even formal methods can have bugs in the specification.

It's good for the compiler to provide correctness guarantees where it can, but tests find different bugs. I think they are useful things to have.

Having said that, I once did an analysis of tests vs bugs in a fairly large code base. There was almost no correlation between number of tests and number of bugs.

Most bugs caught in the wild were actually failures of the developer to fully understand the spec. We had tests that enforced the incorrect understanding!