There focus on 4 main areas as specified in the BS Standard usually around the air vents as they view them as a point of weakness, they mount the helmets onto steel headform and then drop them from a height onto a metal anvil. Force plates inside the helmet record the deceleration by each model of helmet.
The reading have to be less than 250g otherwise the helmet is failed on that specific site, the minimum reading the machine is calibrated to record is 20g.....
50% of the results fell <20g for the Elite helmet
25% for the Premier helmet were <20g......
The other brands didn't have a single reading that fell below this level
This is repeated in 3 different climates...+50 degrees, ambient and UV to give a set of results under the different circumstances and ensure the helmets are safe in different environments etc.