Back when I was playing Anarchy Online, I mostly played on the test server. It was around the time that the new Fixer grid was being implemented. Many people poured onto the test servers to try to get a head start on figuring out how to do the quest that would grant you access to it.
The quest required that you locate and terminate three different mobs (among other steps). They would spawn in certain positions but they would not always be what was spawned there. So sometimes you needed to kill a few other mobs in order to have the proper mob spawn. Players had found the first and second locations but had no idea where the third one was.
Let me take a step back. Besides players, there were also employees (?) known as “Bug Hunters” that would be on the test server. They would take reports from players that found bugs as well as trying to track down problems on their own.
One of them made a mistake. Over the global chat channel, he typed out what looked to be a teleport command and some coordinates. Oops. I went into the normal grid and started popping out at different locations to see my coordinates. When I found a location that was close enough, I popped into my yalm and flew the rest of the way. There was the Bug Hunter and the NPC. He just gave away the third location. He saw me and struck up a conversation.
I imagine I was not the only one to see those coordinates, but I promised the Bug Hunter I would keep my mouth shut (and I did until today, hehe). Sadly, I did not see that guy around any more. Perhaps he was fired, perhaps he changed his character name.
As you can see, there are issues to consider when thinking about a having public test server. Should you put new quests on the test server? Should you have employees testing the quests on that server? This is just one example of what could go wrong.
I think these and many other issues are why most games do not have a public test server. In fact, even games with private test servers (Asheron’s Call 2 Vanguard Program for example) have problems with leaks getting out to the general public. It’s a sticky issue and I’m not sure that I have seen a good implementation of a test server yet.