As of right now, there is no official exact release date, aside from confirmation of summer 2019. It is expected to hit the internet roughly mid-July, or possibly in August. Something as highly anticipated as WoW Classic could launch with weeks of notice and still break records. As of April 21st 2019, World of Warcraft Classic has entered internal employee alpha testing. 

Another hurdle we had to overcome was how to store and merge our data. World of Warcraft has multiple updates or patches in development at any one time, each in a different stage of development. If an art asset or terrain file is added to one patch, the system is designed so that it also automatically shows up in later patches. This meant that If we had simply inserted a new patch for WoW Classic into the current development environment, we would have overwritten things like the current broken dam in Loch Modan with the previous intact version—and as you can imagine, this would have caused issues for Battle for Azeroth.