People often study a subject until they can get 100% right on a test of their understanding of the subject. While this is a sensible approach, it turns out that about 10% of the correct answers are comprised of guesswork, short-term memory, and information not fully learned.
The best approach to measuring your learning is to study until you get 100%. Then wait a day or two and test again. The second test is a much better measure of your grasp of the material.
Testing is important in another important way, in the sense of getting feedback. This can be as simple as pulling on the door you just locked to make sure it is truly locked. For example, Peter Drucker says that quality isn’t what you put into a thing. Quality is what somebody else gets out of it. Therefore, you can’t answer the question of whether your service is any good. Only your customers can. You don’t get to say whether you are a good parent. Your children answer that.
Even more generally, good intentions alone are not enough. Get feedback to determine whether you are getting the right results.