One investigation demonstrated how to test for (reactive) agility (1) - see reference below. The investigation utilized flashing lights as a stimulus when the player ran through a trigger gate. Time was taken from the start gate to the lights.
We believe that testing (and therefore training (2)) for agility is important, however, due to the more or less complicated measurement (different device needs to be synchronized and therefore a lot of equipment and manpower is needed) we never tested players (with scientific standards) due to the mentioned reasons.
If coaches want to apply agility testing and training (and have the necessary equipment available), the lights should flash randomly "left or right". Therefore, the testing should officially use an uneven number, i.e. 5 and therefore 2 left and 3 right to ensure that players cannot guess the direction. However, only the average of two trials each direction will be recorded.
1. Green, B. S., C. Blake and B. M. Caulfield. A valid field test protocol of linear speed and agility in rugby
union. J. Strength. Cond. Res. 25(5): 1256-1262, 2011.
2. Serpell, B. G., W. B. Young and M. Ford. Are the perceptual and decision-making components of agility
trainable? A preliminary investigation. J. Strength. Cond. Res. 25(5): 1240-1248, 2011.