I am in no way supporting this D&A testing, however i would like to make one point.
It is not solely targeting people who will be flying an aircraft. It is possibly intended to catch the bag snatchers and other machinery operators who frequent the apron area.
Accidents invloving these people are common and (with no firm evidence to support this) rumour suggests alcohol and drug usage or influence is a commonfactor.
Point being if you are in what is classed as a safety sensitive area then so be it.
having said that if you are pinged under those circumstances then the tester would need testing him/herself and not for drugs.