>the person who wrote it knows that you have the knowledge to find the answer.
This isn't always true. The person who wrote it only knows what they taught, not what you have learned. The point of the test is to find what you have learned.
This is just a nitpick I think.
Not a very interesting nitpick then. I guess I should have written "knows that you should have the knowledge to find the answer". If we could teach and be sure that students had learned, we wouldn't need to test them.