Checkout nstest from acs-misc CVS. There is a document at
http://acs-misc.sourceforge.net/nstest-manual.html you can read too. There are currently only tests for nsxml and some request processing stuff. I was trying to add some for nsimage, which has relatively easy functionality to test. (At the moment, I'm not sure if nstest is broken or my port of nsimage is, but jpeg size calculation isn't working.)
Patches for modules would probably be fine. I wouldn't be optimistic about an automatic system working with the core; I expect some manual merging will be necessary.
