He did give a reason why testing has to be done by other people -- which was: if you, the coder, didn't catch the bug, how could you, the test-writer, catch it?

He did give a reason why testing has to be done by other people -- which was: if you, the coder, didn't catch the bug, how could you, the test-writer, catch it? Sounds like you had a bad tester. Opposite of my experience. A good tester is a gift from the Heavens.