Drug Test For Welfare

My question is, what is the purpose of the proposed drug tests; to cut welfare costs, or to motivate drug users on welfare to sober up? If the purpose is to motivate drug users to sober up, then I think it's worth a shot. However it would be counter productive if the goal were to cut state costs. As the article addressed "the amount of money to be 'saved' by declaring particular recipients ineligible is still far less than the amount of money required to administer drug screenings to all recipients on a regular basis." Therefore trying to cut costs would ultimately be a waste of time and money.