Perhaps it's already been mentioned, but GroupTalent [1] has set up a business to offer this type of 'small project as an interview,' or what they call "Date a Company" to help guide primarily freelancers to full-time employment:

They did a pivot after acquiring Kyle's TinyProj [2] customer base, which included us. Wondering if anyone has any good experience with GroupTalent?

[1] https://grouptalent.com/welcome/ [2] http://techcrunch.com/2012/01/16/tinyproj-shuts-down-users-s...