[pclowes]

I agree with that but I would say that if I required formal verification of that kind I would move the proof based rationale into the type system to provide those checks.

I would add Tests can be probabilistically exhaustive (eg property based testing) and answer questions beyond what proof based reasoning can provide ie. is this sorting of arbitrary strings efficient and fast?

[joseneca]

Proofs are arguably still better than tests at evaluating efficiency, at least for smaller components/algorithms in isolation. While there are cases where constant factors that can't be described well in a proof matter, in most cases, the crucial element of an algorithm's efficiency lies in how the complexity scales, which can be proven in the vast majority of cases. On the other hand, relying solely on benchmarking introduces a lot of noise that can be difficult to sort through.