When I've interviewed using homework like this, it was with the sole purpose of bringing it along and talking to it. That won't be gamed. And, by the way, that lends itself also very well for bringing whatever fitted in the time box, and having a discussion on the meeting about the tasks that remain, and about their prioritization process. You may like it when you see less production code, in favor of some tests! People coming in with a full-fletched solution, and then to tell me they didn't have time for a test, what am I to make from that?