Here is one of the best articles on the subject I have read. I hope it won't be a problem to post a link since it is a competing site. If it is against the rules somebody nuke it.
http://www.venturers.org/Tech_Library/?action=article&cat_id=002007&id=400
Also I have seen a R/R pass the tests and actually be bad. If it fails it is definitely bad but not failing does not prove it is good. The manual says to test everything else and then decide it is the R/R if everything else passes. At over 100,000 miles I have been through this a couple of times in the last couple of years. The first time it was the R/R. The second time was the stator.