Different qualities aren't limited only to wild pets—many rare World drops and special non-wild companions have had their stats boosted. For example, the world-drop dragon whelps (Azure Whelpling, Crimson Whelpling, Dark Whelpling, and Emerald Whelpling) are of [rare] quality. Check your Pet Journal to see the color-coded rarity of your non-wild pets.
The upcoming stress test will have some limitations. If you’re accepted for the test, you’ll see the launcher offer you a new drop down on the World of Warcraft section marked as “Beta & Stress Test: WoW Classic” which will allow you to download the client in advance of Wednesday’s test, but if you’re not already in the beta you won’t be able to log in until May 22 from 4 to 6 PM Pacific time. If you’re already in the beta, be aware that you won’t be able to log onto the beta realms either, as those will be down while the new stress test realm is up. The purpose is to get as many players as possible into those starting zones to test for stability — so there are some limitations.
The original World of Warcraft was released in 2004, and World of Warcraft Classic aims to recreate the state of the MMORPG before its first expansion, The Burning Crusade, was rolled out in January 2007. Previously, players looking for a “vanilla” version of the game were only able to experience it on custom servers such as Nostalrius, which Blizzard shut down in 2016 to protect its intellectual property.