#1 - Dec. 15, 2015, 9:02 p.m.
Here are the Classes and Specializations that are currently available to be tested on Alpha realms. Testers can swap between available specializations at any time, but will be unable to swap to a spec not on this list.
We will eventually have all specializations available for testing, but as implementation and iteration occurs some classes and specializations will not be in a playable state, and are thus locked out for testing.
Death Knight
Demon Hunter
Druid
Hunter
Mage
Monk
Paladin
Priest
Rogue
Warlock
Warrior