You interview them, just like we do for every unknown person. If you don't want to take the time to do that, then you do a quick search for work they've done, and then come back to the 'do I want to interview this person?' question. Ask them what their timeline for having a job is. Tell them that the interview will involve coding on this specific thing, give them weeks or a month to prepare for it.

Help your candidates do the best they can. Don't set them up to fail at a task they weren't expecting.