You can opt in for the beta at the official site. When the beta launches on May 15, players who’ve gotten in will be able to play all the way from from level one to 30. WoW game director Ion Hazzikostas tells us that the beta will be “uncharacteristically small compared to our expansions,” in part to ensure that the focus is on the proper launch this August.
So committed, in fact, that modern WoW players are trying the beta and reporting what seem like bugs today but what were actually intended functionality 13 years ago. This became such a common occurrence that Blizzard publicly posted a list of known non-issues called the "WoW Classic 'Not a Bug' List." For example, hitboxes for the Tauren player race are much larger than those of other races. In a modern game, this would be seen as a serious balance issue (see: Apex Legends). But it's what vanilla WoW was like, so it has been faithfully reproduced.
Bioelectric Blast (Deadly) - Blasts the target area with electricity. Inflicts 65,654 Nature damage to enemies within 8 yards of the impact and creates a patch of Electrified Ground. Electrified Ground inflicts 14,882 Nature damage every 2 sec to players within it. Shock Burst (Important) - Inflicts 4,377 Nature damage every 2 sec for 12 sec. Upon expiration, strikes all players, inflicting up to 26,261 Nature damage. This damage is reduced the further away players are from the blast. Electric Discharge (Healer Alert) - Wekemara discharges electricity from itself. Inflicts 13,131 Nature damage that chains to additional targets every 1.5 sec. Submerge - Upon reaching 50% health, Wekamara will submerge and summon Spawns of Wekamara. Electrified Splash - While submerged, Wekemara rains electrified water from its pool. Inflicts 21,885 Nature damage to enemies within 3 yards of the impact area. Spawn of Wekemara (Damage Dealer / Tank Alert) Charged Bite - Inflicts Nature damage to an enemy Conductive Spittle - Inflicts Nature damage to an enemy and increases Nature damage taken by 50% for 16 sec. Loot Tables