I don't know, but the one thing I will say is that they're often interesting, or at least some of them.

I tried one, and I've seen it since, which is a challenge i.e. they'll present you with a basic page saying "Try JSON", or something of a similar ilk. Then you have to follow the rabbit hole (automating a solution in a scripting language generally) until eventually you're met with a page with actually how to apply to the real job.

I like companies that do that.

The one I saw the other day was a grid of dots (say 300 or so), with some filled in. They gave you one second to count the dots and submit the form, so the trick is parsing the HTML in < 1 second and responding within the session.

Edit: You'll have to switch up the game now hehe.