Actually, we are evaluating the dog's retrieve drive. The drive must be so over the top and insatiable that the dog will HUNT for it under any and all circumstances. You start out in an area with weeds,tall grass,debris whatever. You throw some sight retrieves. Then you set up blind retrieves. You place the ball,kong, bumper whatever out in an area,bring the dog and "fake" throw the reward. The dog must go out and search NONSTOP for this without becoming distracted or bored.
If the dog accomplishes this,you move on to other environments. You continue the blind retrieve exercises making sure the dog never stops searching. Test dogs around loud noises, distractions, on rubble or debris, on slick floors. etc. ANY sign of distraction from searching,the dog is a wash
Drive cannot be built. It is there or it is not. Genetics