The Wizard101 Test Realm is set up by KingsIsle to test new material for the game.
It is only available sometimes, and when it is available it is only for subscription players or for those who bought more than $10 in Crowns in the last 30 days. Information on gaining access is at https://www.wizard101.com/game/testrealm .
Each time you access the Test Realm, you get to use a backed-up version of your live realm character that has 250,000 Crowns. Each time it closes and re-opens anything you obtained in the test realm is lost. Note: NOTHING from the test realm carries over into the live realm.
PLEASE DO NOT POST TEST REALM INFORMATION ON THE WIKI. The information changes too much before release into the live realm, anything posted will be deleted.