It all started with a game design update back in May where Blizzard hinted that there will be a PTR for upcoming patches. The PTR option link has now been enabled in the launcher, but for now it only redirects you to the Battle.net page.
» Source:Game Design UpdateWe’re going full steam ahead on the PvP patch, which will also include a number of game changes unrelated to PvP, and we look forward to sharing more about that as we get closer to opening up a PTR, where you’ll be able to test out our changes -- and enjoy mercilessly slaughtering one another in the PvP arena.
As patch 1.0.5 is coming soon™ in which there will be changes to classes, skills and the improved Crowd Control system, it's a good bet that we will see the Public Test Realm active either before or following this patch release. We might not get PvP on the PTR right away, but it should not be too far off.
So all we can do now is wait for the Patch 1.0.5 blog update and cross our fingers that we can get our hands on the PvP soon.
As soon as the PvP PTR is up rest assure we will cover it in depth with all classes and how they fair against one another and some build tips.