World of Warcraft players who want to get an early look at the v5.2: The Thunder King will want to check into the public test realm to take the new patch for a spin. The upcoming patch includes a new raid dungeon, pet system improvements, a new quest hub, and much more.
Patch 5.2: The Thunder King is now available for testing on the Public Test Realms! By logging in you can help us test a massive new raid dungeon, a multi-faceted new quest hub, Pet Battle improvements, new world bosses, significant class balance changes, brand new pets and mounts, assorted bug fixes, and more. If you'd like to help test and provide feedback, you can start by copying your character and downloading the PTR client. Once you've had a chance to try things out, be sure to visit our PTR Discussion forum to discuss the patch, and the PTR Bug Report forum to report any issues or errors.
Check out the patch notes on the World of Warcraft community site.