Tests are the primary way we evaluate students. In standard instruction, a test comes at the endpoint of teaching and learning. We teach something, students try to learn it and then we test them to determine what they know. However, testing can also be a powerful way to enhance student learning. For nearly 100 years researchers have known that when people try to recall what they learned previously, it improves their learning. This is known as the test effect or test enhanced learning.
For more information watch the attached video and also see Test Enhanced Learning.