I can't answer for your parent, but for me it is the following. The main purpose of a test suite is to detect regressions in intended behavior. In a good test s

I can't answer for your parent, but for me it is the following. The main purpose of a test suite is to detect regressions in intended behavior. In a good test suite, if a test fails, then I can be sure that some part of the actual system would fail if I push this to prod. Since the set of intended behavior is only a small fraction of all actual behavior, if your test suite pins down all actual behavior, rather than just the intended behavior, you end up with a very brittle test suite. That is to say, a test failing doesn't tell you "this code is broken", it just tells you "this code changed".