[jeffbee]

Sounds like a very smart person. Much of the value in the test is showing that the old revision fails it. If I were fixing this bug, first thing I would do is write the test and make sure the existing code fails. If it doesn't fail, that means I don't understand the problem yet. Then I fix the problem and commit both the fix and the test. I don't just discard the test, because it is valuable to know that in the future nobody re-introduces the exact same flaw (this regularly happens in open source projects).

[gnunez]

I agree. Keeping the test around provides a safety net (a bug repellent of sorts) for the next person the comes along. The test also serves as a documented history of the bugs of the past. The problem is that test does not guarantee the injection of future bugs of a different type. I don't think any amount of testing will. That's not to say we shouldn't write test, we should just be aware of the limits of testing.