Stopping Distance
I can answer one part of your question:
To obtain stopping distances, they perform 'max performance' landings under near ideal conditions - basically plant the airplane on the runway and then stand on the brakes (no thrust reversers) - and measure the stopping distance. That's done at various weights and landing speeds.
A factor is applied to the resultant stopping distances (my memory says 1.6 but I'm not sure about that) to obtain the cert stopping distances.
Of course in the real world you get things like wet/contaminated runways and less than perfect landing techniques - with some compensation provided by use of the reversers. The factor they apply is intended to account for that.