I took one 17 years ago (when I was 17 yo) because Loss Prevention was accusing me of stealing car stereos at a store I worked at. The woman doing the investigation was damn sure I was the one and would not lay off until I agreed to take one. I passed, but I was soooo damn nervous. While I don't think they are anywhere near infallible, and should not be allowed as admissable evidence in court, it was correct in my case, thankfully...
The test consisted of questions specific to the stereos as well as ones like "Have you ever stolen anything in your life?"