I had a similar requirement and i placed such files in server/default/conf. That worked for me.
That works great!
This info should be on the front page on "JBoss for dummies"...
I suppose this not necessarily implies that /server/default/conf is in the classpath?
An other approach would be to create 2 ears (one prod, one test), using Ant for instance. This is what I use to do, my build script would create each WARs, JARs EARs etc. with appropriate config files for the 2 environnements.