My stepson is on probation for theft for a year. He is 5 months into it. He is a drug user and has not quit.

He got a new probation officer yesterday, and he asked my stepson if he could pass a drug test. He answered that no he could not. But did NOT test him!
That was the first time he'd been asked about drugs or testing.

WHY would they NOT test him?? The kid need to suffer the consequences of his actions, which will hopefully lead him to sobriety!

Often such a question (cops do it on traffic stops too) is a test to see how honest someone is, an important thing to know going forward.

Why he hasn't been tested yet (your second question) is between the courts and him, with discretion of the PO. We don't know his age, history, or the nature of the theft. We don't know how eager he is to stop stealing and to quit drugs. He said he wouldn't pass so what do you feel would be the benefit of proving it?

If he's over 18, try to let him take charge of his own life. If he still lives with you and his father, then talk (all 3 of you) about the rules of the home and whether or not he should remain there.

With all that is going on, kudos for him being honest. Sadly honesty is becoming less and less the norm.

He's 19, flunked out of college first semester to do drugs and wasted $20k of our money in the process.
He still lives at home(with his mother). He works minimal hours as a grocery bagger and blows his checks on blow and designer clothes instead of paying his car payment, insurance, food, phone bill, gas money. And his Mom covers all that for him. She is a big part of the problem.

He has no desire to change - because he's living a cush life on a silver platter with no end in sight.

He was charge with felony theft at Walmart. He plead down to a misdemeanor, for 1yr probation, no jail time. A failed test would violate that and put him in jail - which I think he would consider "rock bottom" enough to straighten his life up!

Some men take some time to grow up and it is very frustrating as parents. Granted if the mom covers him on everything she's being no help to him. This boy needs a structured life until he can provide structure for himself. Free time and no responsibilities will not help him growing up. Also being completely negative to him on everything won't help either. But I know that it's difficult to point out positives in his life when there is so much negative.

He was a very sweet natured young man... until drugs. Now he is hateful, violent, and a threat to himself and others because he drives falling down drunk and high all the time. And yet, his mother still is providing a car for him to do so. Definitely not doing him any favors. We haven't seen him for a year. We live long distance, and he's not talking to us because my husband isn't supportive of his new "adult" lifestyle choices. I guess anyone that disapproves gets cut out.

Back to the original question though, the probation officer didn't do him any favors either by giving him a free pass.

Going to be a bit harsh now - it's NOYB. He's an adult. He lives with his bio mother. His father, your husband, doesn't approve.
If anything, this is between you and your husband. But why is it your issue at all? It isn't. And if both marriages broke up and new spouses were found at some stage of the son's life that affected him adversely, it might have set the stage for a life of dissolution and anger, pretending not to care anymore.

I tried to explain that many variables go into decisions about parole.
Someday he may very likely be arrested for drugs. He hasn't been yet. If he lived with you, you could probably call the cops on him for doing and having drugs in your home.
Until he is arrested for a drug crime, there's no point second guessing how the courts and parole systems work.

You have to wait and see what the new PO does with his honest disclosure, a process that may take time to bear fruit. I am sure he will be the first to know if there are changes or added conditions to his probation, likely up to a judge to decide.

How does someone get $20K of YOUR money without your consent? His mother is looking for a huge lawsuit if he gets in an accident .

Because no one, including the courts want to put him in jail for a misdemeanor theft. Also drug testing may not have been part of the probation order.

This is a easy issue, demand that your wife, kick him out. Start keeping your money separate from your wife, if she is supplying him money.