What is the purpose of a personality test?

Think of a personality test creator like an interviewer and the test taker as their interviewee. An interview works best if both parties know its purpose, understand the questions and answer them honestly. The same goes for personality tests.

Granted, there have been 'personality tests' trying to trick people into indirectly giving away their secrets. For example, some tests have asked people to tell what they see in ink blobs, supposedly revealing their hidden thoughts and feelings. Other tests have used obscure questions with no apparent relevance for personality, like “My mother was a good woman.” But there is little evidence that such trickery provides much useful information.