"You always know when you have a good tester, because you're always a little annoyed when that person comes around your desk/cube. The reason for this is that you know that if the tester is in your general vicinity, they've found something wrong with what you've written. All the excuses start to pile up in your mind of 'Well, you're not using it right!', etc, but in the end, you know that the tester is right, and you've just made a mistake in your programming."
-https://stackoverflow.com/a/525673