I came here just to make the opposite point. They aren't making you do a test, they're hiring you for a project. It's fine if you're too busy even for paid work, but why would you turn it down otherwise?

I think Joel means "unpaid tests". I routinely turn interviews with unpaid projects down, because each interview process gets a number of hours of my time for free (depending on how much I want to work for that company) and unpaid tests/projects usually way way overrun that time.

Or maybe that's what you said and I misunderstood?