Reliable tests are those that consistently give the same results. A good test will not say that you are a strong extrovert one day and say that you are an introvert the next. Valid tests are those which measure what they say they are measuring. For example, if a test claims to measure intelligence, it should be related to academic performance. Standardized tests are those given to everyone under the same conditions so that your results can be compared to results of others who have taken the test.
Agencies request many different types of tests.
They may want to know about a person's cognitive ability, most commonly in the form of some intelligence test. Aptitude tests give some indication of a person's potential to learn something, such as another language. Achievement tests measure what has been learned. To help place people in positions where they will be happiest and most effective, agencies may requests tests of interests, personality characteristics, abilities, skills, and work values. To learn what people are like, agencies may request personality tests.