The test servers are/were for the initial opening of the game (or any game for that matter) You had to sign up to be a tester when the game first came out in Beta. Sometimes mmo's will call out for new testers when new content is planning to be added, and if you catch it in time, you may be asked to become a tester. Some games have waiting lists a mile long to get into the testing though, so don't hold your breath
