The Wrath of the Lich King Classic Beta

Blizzard announces beta testing of The Wrath of the Lich King Classic is now underway. If you opted in but haven't received an invitation, more invites will be sent out over the course of testing. There's also this update from the development team on how rereleasing this classic World of Warcraft content provided the chance to improve gameplay in several areas. Here's more on how to get invited:
The Wrath of the Lich King Classic beta test has begun! Over the course of the test, we’ll be inviting opt-in beta testers and more to check out the upcoming Classic expansion and give us feedback.

Players selected to participate in the beta test will receive an email invitation directing them to download the beta client directly from the Battle.net desktop app. As always, please be aware of phishing attempts—if you’re unsure whether your invitation is legitimate, please log in to your Battle.net account to verify that there is a Wrath of the Lich King Classic beta license attached (under Your Game Accounts).