[gshulegaard]

> If the dev didn't handle the case in code they're not going to know to test for it. Fuzzing is a much better approach.

I routinely call myself a proponent of BDT (Bug Driven Tests) over TDD for much a similar reason. That said, tests are HUGELY beneficial for guarding against regressions and ensuring effective refactors. Anecdotal but on my current project tests helped us:

* Catch (new) bugs/changes in behavior when upgrading libraries.

* Rewrite core components from the ground up with a high degree of confidence in backwards compatability.

* Refactor our Object model completely for better async programming patterns.

I don't think tests are particularly good at guarding against future bugs in new features; as your comment about fuzzing hits squarely on.

But I DO think tests are good at catching regressions and improving confidence in the effectiveness of fundamental changes in design or underlying utilities version to version.