It is believed that a valid psychometric test is one that meets three standards: content validity, criterion validity, and theoretical validity.
In a nutshell, content validity is the answer to the question of whether the questions correspond to the behavior that describes the feature we want to measure. In the case of a sense of humor, the question of whether I like to walk fast or slowly will be irrelevant, and the question of whether I enjoy jokes will be valid. Criteria for validity is, for example, an actual diagnosis that is confirmed in the future: someone actually has a sense of humor and the test diagnosed it. Theoretical validity is compliance with the definition, e.g. a sense of humor.
