It's a completely stupid situation, because programmers are simultaneously bad at tests and (in theory) much more expensive, so telling them to perform tests like that is a waste on every level. Joel Spolsky warned about that 16 years ago:

Joel on Software

Why testers?

My sister got her kids a little puppy, and they’ve been trying to train it. To live with a dog in the house, you need to teach it not to jump on ...