They are really quite different jobs. The devs on my team (at Microsoft) write their own unit tests and are responsible for the quality of their code. The test

They are really quite different jobs. The devs on my team (at Microsoft) write their own unit tests and are responsible for the quality of their code. The testers, however, own sign off. The tests they write are significantly different: they involve testing the product as a whole instead of just a single module. Especially in large GUI applications, such as Visual Studio, testers have the extremely challenging task of automating tests for high level end-to-end scenerios. I'm not sure if I have an opinion of what the "correct" ratio should be, but I do know that it is a good idea to have the person saying "OK, we can ship this" to be different than the person saying "Yeah, it works for me!" When you work on web software and customers start complaining about your shoddy update, you can issue a patch before the end of your coffee break. When you press your software onto millions of disks and promise to support those bits for a decade, you better be damn sure it works and meets the requirements.