Just in case there are others out there that were assuming their Beta opt in for World of Warcraft also included Classic I thought I would point out that it apparently doesn't. I stumbled across this fact while browsing the wow forums for updates on the beta.
To become a tester for the WoW Classic Beta: browse to the Battle.net Beta Profile Settings, find and select ‘World of Warcraft Classic’ under ‘Beta Tests I’m Interested In’, and then click the ‘Update Preferences’ button. An automated system will add new testers to the WoW Classic Beta Test as necessary.
I've just done this now, but wish I had been made aware of this before so I could have opted in at an earlier date. Oh well.
Classic WoW Testing Schedule
Beginning May 15, select WoW players will be invited to participate in a small-scale, focused closed beta test. Players will also get a chance to help put our servers and technology through their paces in a series of stress tests running from May through July—you can opt in now through Account Management and select the WoW Classic beta. Subsequent stress tests will extend the opportunity to even more players. Level caps will also be in place to ensure we’re emphasizing the “stress” in “stress test”
—we want to push our tech to the limit, and that means a critical mass of players in close proximity.
STRESS TEST SCHEDULE*
Stress Test 1: Wed May 22–Thurs May 23
Stress Test 2: Wed Jun 19– Thurs Jun 20
Stress Test 3: Thurs Jul 18– Fri July 19
*Dates of each stress test are subject to change.
To fill our pool of beta and stress test participants, we’ll be choosing dedicated players who meet select criteria from both the WoW Classic beta opt-in and the standard Warcraft beta opt-in. Participants will also need to have an active subscription or active game time on their Battle.net Account. While opting-in to the beta is the primary way to make sure you’re in the running to join the test it doesn’t guarantee an invitation to the closed beta test. We may also consider additional factors such as how long a player has been subscribed to the game so that we have the right mix of players to ensure great feedback toward making WoW Classic the very best experience for the community.