Linden Lab recently contracted i3DNow to develop a test harness for inworld testing of LSL. We will use this harness to ensure LSL functionality across releases. As we started working with the harness we realized that it's just too good not to share with the developer community.
So if you want to use this harness to check your own scripts with each new SL version, just go to https://wiki.secondlife.com/wiki/LSL_Test_Harness. You will find links to all the LSL code for the harness, as well as some simple instructions on how to set it up.
Basically you create a couple prims, cut/paste the code from the wiki into them, and add your specific tests. The harness responds to chat commands to register test units, conduct tests, and issue reports. For those who want a more pushbutton interface we have also included the code to build some buttons which duplicate the chat functionality.
Cheers, and happy testing,
Periapse Linden