Current learning theory suggests that tests that require mental operations on factual material are more likely to lead to longer term learning. And where a correct answer does require significant thought and procedural knowledge, it cannot demand of the student inventive use of language to express ideas. And it is just this way of using language to express ideas that should be a significant outcome of education. One important function of testing is to let the student know if he or she has mastered material. For this to work, tests have to be returned promptly, while the material is still fresh in the student's mind.
Prompt feedback is important to learning.
Feedback from tests, then, is another component in helping students to learn. In sum, testing should be seen as an integral part of the learning process. Using CAT's frequently to assess learning lets the teacher know if he or she has succeeded, and also helps students monitor their own learning. Some teachers pride themselves on giving tests that are so hard, few students can pass them, but such testing doesn't lead to learning. Tests should demand thinking as well as recognizing.