That's because it actually doesn't need much testing?
Talent trees have already been broken down why they essentially require the bare minimum of testing.
Crafting system needs testing.
Reputation moving towards reknown doesn't require testing since it's using the existing reknown infrastructure over the base reputation you'd normally see. Functionally the same but visually different is all.
The biggest changes are the talent trees and crafting system and only one of those requires actual testing. Assuming Blizzard didn't lie back in April that they're ahead of schedule/further along in development compared to past expansions, 5 months of testing is plenty.