I'm not arguing for black/white box testing, I'm arguing that for testing to have real value, your tester needs to behave in a similar manner to a real user. Th

I'm not arguing for black/white box testing, I'm arguing that for testing to have real value, your tester needs to behave in a similar manner to a real user. That way you find the gap between your own understanding and your users' understanding of the system. Take a concrete example: a piece of medical equipment prints off reports. If your tester has no medical knowledge, he doesn't have a frame of reference to know if the numbers are correct or not. He's also more inclined to use it exactly how you specify. A real doctor would bring his own experience of similar equipment and try to use it in ways you didn't think of. In addition, he will be able to gauge whether the reports "look right".