The latter. Also misunderstandings about APIs. IME these combined are usually something like 70% of all bugs so the ROI on unit tests is not particularly high.

The latter. Also misunderstandings about APIs. IME these combined are usually something like 70% of all bugs so the ROI on unit tests is not particularly high. I find integration tests paired with BDD do a good job of catching "code plain wrong" bugs as well as misused APIs and misunderstood specs. They're harder to build and run slower but the ROI is still higher.