@JPB,
Misuse of drugs when you have children, adopted or not, is reprehensible. To me and many others, use of so called recreational drugs is not in itself a bad thing, no matter the legalities at present. In my experience, a huge percentage of the people I knew in the sixties and seventies used drugs of some sort, including alcohol, which certainly can be abused, though legal.
I'm firming up on the side of NO. I can see individuals being tested for cause, but not when applying for Tanf (whatever that is) if all other qualifications are documented in some way.
I do know of a child, one dear to me, whose mother spent her child support money on drugs and had the child 'farmed out' to questionable friends. I didn't learn this until later or I'd have been riding a horse into a courtroom. The mother was a piece of work, which I don't want to go into. But in that situation, there should have been more oversight, starting with the dad and an attorney.
As much as I know the ill effects of possible expenditure of the money on other than the child, I can't subscribe to blanket testing of all applying for tanf.