Bicycle Quarterly does rolling resistance tests on tires all the time. Go to their website, look for the issues with tires tests, and buy a couple of back issues.
The BQ tests seem to be very carefully done.
As I recall, they put the tires on real bikes and they roll down part of an old Soap Box Derby track. That gives them the quantitative data they have. They also then test ride the tires and render a more "qualitative" assessment as well.