Although augmented reality is not quite mainstream yet, with Oculus rift prices rapidly lowering and variety of new hardware and software options such as the Hololens and the new Macs coming with Steam VR Support, the future is rapidly approaching. How can we as UX Designers prepare ourselves for this shift? How can we anticipate a future need that isn't quite here yet? How do UX Design methods translate into visual space? Here's a quite thorough list of articles that answer some of these questions: https://www.uxofvr.com/ .
User testing can be conducted in much the same way regardless of whether we are talking about architecture, websites, augmented reality, or the Holodeck. Things that are working and not working, satisfaction levels, navigation speed and clarity, eye tracking, all of these things will be tested in much the same way. Although there isn't any SEO for VR that I am aware of as yet, I'm sure there will eventually be systems in place for tracking and tagging what a user does in virtual space.
What will be a huge difference is the interaction design, menu navigation, and spatial use. Particularly without any standards and each product having its own world layouts, input methods, and interaction styles. It really is the wild west at the moment and designing for it is an exciting challenge. Rapid designing for AR/VR/MR 3-D spaces requires some advanced out of the box thinking and when drawing, a special kind of spatial mapping and perhaps quick video illustrations of interaction ideas.
One of my professors at NYU, Sung Park, had us do these sketches [example below] and has been co-developing a curriculum to address these up and coming virtual reality opportunities.
Test of a 3-D sketch layout. The clouds aren't quite right...