The testserver is just there to test the features that are about to be released to the game server. So the most nasty bugs are squished before they hit the game server.
You find a list of the current testing targets on the main page right below the testserver status or using this link: http://illarion.org/development/mantis_ ... r_bugs.php
. These are the thing we currently like you to test. You should attach your findings as comment to the mantis tasks. You also can test other things on your own. In case you run into other strange bugs you should also report those to mantis and tag them with the "testserver" tag.