As others have described, they ask you to complete a work sample which is fitting a linear model to noisy data. Contact person, who was at first rude over the phone, convinced me to do it. After spending a lot if time on it, I submit and two weeks later hear there is no fit. No explanation why; they want to "protect the integrity of the test". Not at all helpful. Surely there is some feedback they could give without revealing what they view as a good answer. Too long, too short, not enough detail, invalid assumptions, whatever.