Comment by gridspy

The actual problem is that no-one had considered that this (desync between front and backend) COULD happen. Once it was realized that it was possible (and worth testing) the bug was practically solved already.

Such is true for many bugs. Even if you have unit tests, they only test on things you've thought of. It's usually the stuff you haven't thought of that gets you.

No reason not to unit test of course, but don't get a false sense of complacency or assume testing is easy either. That's why it's great to do things very carefully (and probably not with AI Agents).