[RiderOfGiraffes]

Same problem here:

http://news.ycombinator.com/item?id=994358

It's the unknown and unanticipated failure modes that cause the worst problems. Predicted failure modes at least have code to deal with them, even if it's buggy. Unit tests reduce the bugs, but non-existant code for unanticipated failures, while it doesn't have bugs, doesn't solve the problem.

[caf]

This is why it's a really good idea to have the unit tests written by someone who didn't write the code being tested.