Software testing - frame of mind

I was reading a book recently and I ran across the following quote, which I think comes from Bruce Tate:

Think of a unit test as another client of your application.

That resonates for me on many levels, and it's a great way to think about test code. I also like the following quote, but that may be because I said it:

I know this code is wrong because I can't test it.

Yours in unit testing. ;)