If they are really hiring, the interviewee should do it. If he can't sense whether they are really hiring, he shouldn't do it. But it should be preceded by some

If they are really hiring, the interviewee should do it. If he can't sense whether they are really hiring, he shouldn't do it. But it should be preceded by something else first, such as fizzbuzz. And that said, it should be shorter than a day, but still, if they're hiring he's there because he wants the position, and this is an excellent test.