What are you guys ' opinions on personality tests?

Back in school, there was this girl who would never stop talking about personality tests.

She ultimately managed to convince 'me' to take a few of them, but when 'I' did, it felt sort of weird and 'I' vaguely remember getting a massive headache which I guess was kind of worse than usual. 'I' didn't want to spoil the mood though (and may or may not have felt like 'I' couldn't really tell her because she seemed just fine :D) so 'I' simply asked her why she liked them so much. She was like: "Well, they're just super important because they define who you are and they help me understand why I am the way I am." ...

...and for some reason, that very sentence led 'me' to obsess over them in a way one would consider unhealthy. (Despite them usually causing some proper inner turmoil - not just in 'my' own time, but in therapy as well.:D)

So yea, how do you guys feel about them?