What a lousy idea.
Libertarians have always opposed government welfare, because it forces people to give up their money involuntarily to others. Even worse, it can trap recipients in a cycle of dependency.
Sadly, some conservative Texas legislators want to compel taxpayers to pay for drug testing on top of it. You sometimes get the feeling that conservatives just love offending the dignity of people like welfare recipients.
The answer to a bad program like government welfare is to get rid of it, not to pile new restrictions on top of it.