I remember Steve Maguire saying this in Writing Solid Code (that they're both necessary, and both types of testing complement the other). He criticized Microsof

I remember Steve Maguire saying this in Writing Solid Code (that they're both necessary, and both types of testing complement the other). He criticized Microsoft employees who relied on QA to find their bugs. He compared QA testing to a psychologist sitting down with a person and judging whether the person is insane after a conversation. The programmer can test from the inside out, whereas QA has to treat the program like a black box, with outputs and effects resulting from certain inputs.