Would be good to hear how many people would accept to work on a design test for free. A recent job i have applied to seem to want quite a bit of work for nothing, previously i have only done test that have been paid.
Depends how badly you want to work there right? I've done a few and they were all unpaid to be honest. If I'm interested in a job and I want to prove them I'm good enough to work there I'm willing to do a unpaid test if it's reasonable in size. Obviously not weeks worth of work, but I've done some that took 2-3 days.
Out of principle before i have said no as there were too many times i saw alot of people being interviewed and tested to solve problems the company were trying to solve at the time. In theory every hiring round they received a bunch of free UX/UI ideas for the product.