[JamesBarney]

I think domain knowledge is the most important quality of a good manual tester.

We've had great luck with testers that moved from users to testers. We had a nurse testing as a tester on our clinical app and she was invaluable, we had a geologist testing our seismic applications and she was also invaluable. They also focused on what issues were important in an app, and were great at prioritization.

And we've had cross-domain testers, and they were not as valuable. They seemed to be more nit-picky because they didn't have the domain knowledge to judge what was truly important and what wasn't.

What makes a good automation engineer is pretty similar to what makes a good software engineer.

[greenyoda]

I agree that domain knowledge is essential. Without domain knowledge, testers may spend way too much time testing insignificant scenarios which a user would be very unlikely to perform, while missing obvious problems that every user would run into.

Overall, my experiences with testers has been positive. As a developer under constant time pressure, it's very easy for me to make stupid mistakes that end up causing grief for users. Since unit tests (or any tests written by a developer) can only test scenarios that the developer has actually thought of, it's good that someone else is testing the product from a user's perspective that's not biased by preconceived notions of how the code should behave.