Not long after the live realms come back online, the test realms are scheduled to go offline. They'll be down between 2:00PM and 4:00PM PDT for some maintenance. Also, one of the realms will be moving to the "Oceanic" tab (no news on which realm will be making the move) for further cross-realms battlegrounds testing. Haven't had your chance to test yet? Well, you've got at least another week before there's a chance to roll out the patch on the live realms, and the test realms are a great opportunity to give new talent builds - or entire classes - a good try to see how they work out. Plus, it has the potential to be a lot of fun.
Update: The test realms were late coming back online, but they all seem to be back online as of 5:42PM PDT.