I've seen a few of these. Just got a proposal today and here's an extract from the email:

"We like to see a test sample of work on one of our stages before we officially commit to bringing anyone on.
If your test piece is accepted, we can add the hours already worked into your first payment.
If we don't think that you would be a good fit then there is no compensation."

I never know what to do with these. I hate the idea of doing work that could just be someone fishing for free designs. Does anyone else encounter this?