I think it's important to be tested - because for an employer, your book can be pretty, but he has no idea of how it was done (di you work with a team, what did you really do, how did you manage your schedule, etc). With a test, even without a lot of specs, you have an idea of the creativity, reflexion, and delay a candidate has.

Otherwise, I think it's really important to trust the company. I mean, there is some companies for whom I won't do a test since I know they will use it without my consent (well I don't apply for this kind of companies but well).

At my current company, we both signed a document that attested the confidentiality of the specs and the no-use of the work I produced. I think that's how things should be done every time.