#0 - May 20, 2010, 2:52 a.m.
http://www.blizzard.com/support/?id=eHacks000
Try to provide as much information as possible when reporting a player using hacks (date, location, etc).
Taken from the PTR Forum Info and Rules Sticky.
• Q. I saw someone cheating what can I do?
A. The Terms of Service agreement for World of Warcraft applies the same to the Test Realms. http://www.worldofwarcraft.com/legal/termsofuse.html
It is a common misconception that because there is no standard GM support on the test realms that there are no consequences for cheating, this is untrue. We actively remove players who are cheating or otherwise acting inappropriately on the test realms. Actions taken against players who do not follow the terms of service will be quick and severe.
Players who suspect cheating of any kind should report it via the Blizzard support webform located here: http://www.blizzard.com/support/?id=eHacks000
[Edit: Grammar] =P