Yeah it can be, but you'd really prefer to know without having to go do an exhaustive search I think. The closer to the root cause you catch the problem the easier it will be to tell what happened. Plus, it's not always easy to run exactly the right tests and to run them at exactly the moment they're needed. I usually won't run the whole test suite on each commit if I'm just doing a rebase, say, but it would still be nice if I didn't sail past a problem that I would later have to retrace my steps to fix.