They already said they'll be implementing a test server. If you want it RIGHT NOW, though luck.

By the way, the login issues appeared simply because the servers were hammered. That's not something you reproduce on a test server.

They are doing changes with "baby" steps simply because developing and implementing them takes time. Not to test them.

They're not trying anything just in the live game (and if you think that they are you're out of your mind), they have their internal test team, but as the history of MMORPG demonstrated for a thousand times, bugs slip into live releases. Guess what? They do whether a test server exists or not.