Yeah. That would be my answer if I had to pick just one. Tests should give you immediate feedback if you're wrong. They might not tell you exactly what to do. I

Yeah. That would be my answer if I had to pick just one. Tests should give you immediate feedback if you're wrong. They might not tell you exactly what to do. I think there's a bit more to the story than just tests, or I wouldn't have been so elliptical in my comment.