What are the two tests for mental competency?

One test is the cognitive ability test. Under this test, a person is mentally incompetent if he is unable to comprehend the subject of the contract, its nature, and its probable consequences. He need not be proved permanently incompetent to avoid the contract, but his mental defect must be something more than a weakness of intellect or a lack of average intelligence. A second test, recognized by the Restatement and some states, is whether a person's mental condition impairs his ability to act reasonably. The person understands what he is doing, but he cannot control his behavior.