in reply to The Evil Pleasures of Unit Tests
I, for one, see nothing wrong or evil about this. I believe that I remember reading something similar to this on Joel On Software. His take was that you should bury poor programmers on your team with bug reports. The result is that they will either improve or leave.
Also, regarding some of the other comments above, just because someone is on your team doesn't mean they should not be held responsible for the problems they cause. Adding additional tests is somewhat of a backdoor way of making them responsible, but, if all else fails, I'd think it is a very appropriate way to get someone's attention to their poor code.