Are internal 'Patchwerk" tests done?

We do lots of internal testing. However our testing can only go so far. You guys are clever and there a lot of you. It's not uncommon for players to find a totally different way to approach a problem (even if it's as simple as surviving through a dangerous but simple boss). Players might find different gear combinations or talent builds or consumables or raid comps or whatever that allow them to succeed or fail in situations that we didn't predict. We sometimes make mistakes so it's nice to see when our conclusions are supported by "real life" observations. When the player's experience differs from our own, we like to try and figure out why.

Player testing is a supplement to our testing. Few smart companies are arrogant enough to think that their own methods are foolproof.

Q u o t e:
With that said - why did it take as long as it did for you address several of the DK concerns brought up by the very people you are asking help from? From what I can recall - people had a jump on problems the DK class was going to bring to the game long before the problems were addressed.

That's a hindsight is 20/20 thing. There were also a lot of threads about how druid tanks were done for with the armor nerfs. Many of them had math and tests to back them up. In retrospect, that didn't end up being a big issue. Before Ulduar shipped there was a lot of concern that the DK nerfs at that time (based largely around Sartharion) would doom them. That never happened. Players now may say "See, you should have listened to us!" But what we don't see is the players that were wrong typically coming back to post "Oops, we were wrong" (though some do).

Despite what you might read on the forums, even the imbalances that exist today typically don't lead to huge problems. If you take say the top 100 guilds in the world, most of them have the same MT they've always had. They might swap out on a fight or two (which also isn't the worst thing in the world from a design perspective) but the mass tank reroll is pretty oversold on the forums. This isn't to say there aren't balance problems we need to address, but we are in a lot better shape that at any point in WoW's history with regard to tank equity.