Beta testing is now underway for the multiplayer aspect of StarCraft II: Heart of the Swarm. Blizzard recently announced the start of testing and posted a lengthy FAQ on how you can be a part. The quick version – you can opt in through your Battle.net account for possible selection based on testing needs and system specifications. Additional beta opportunities will be provided through giveaways at various fansites. Mac users will be able to participate and the currently supported testing languages will be provided in English, German, French, and Korean with the possibility of more to be added later.

Source: StarCraft II: Heart of the Swarm Beta Announcement