I know someone who studied for the Myers-Briggs test. Really. He figured out which personality traits the management team was looking for to fill a newly-opened supervisor position, and figured out which way to answer to get the results they were looking for. If Manipulative Obsequious Weasel ever becomes an actual job, he's set for life.
He got the job. I mentioned to management that he was going to be there just long enough to grease other palms and make himself known to upper management, then move to something else. They said he was a great fit and wouldn't do that at all. Six months later, I got to have an "I-told-you-so" moment with them.
This guy was an all-out suck-up as long as he wanted the supervisory job. When he got it, and set his sights on the next thing, everyone he sucked-up to was left on the ash heap.
I took it toward the end of my career and it told me that I should be doing what I already had done (career wise). It was satisfying to see that what I liked (and was good at) was exactly what the exam said I should like.
Probably not a good idea for a company to administer the test to a job candidate...too easy to fudge.