As long as you are on probation, you are at risk of random drug and alcohol tests. There is no way to calculate the odds, because anything that increases the concerns of probation also means more chance of being tested. If you use drugs, you are at risk of a probation violation and another case, so consider quitting it all for now
The simple answer is...possibly. As a condition of your probation you likely had to agree that you would submit to random drug and alcohol testing. You didn't mention whether this was your first DWI, or whether you have ever used illicit drugs. This is relevant to your "chance" of being tested. If your answer to the previous query is yes, then the possibility of random drug testing will likely be greater than if the answer is no. Make no mistake, however, that the possibility still exists in either instance.
Also, random drug testing does not mean that if you are tested once, and it comes out clean, that you will not be tested again--you can be tested at any time and it will not be at a convenient time to you!
It is not worth the risk of a probation violation and the negative consequences that go along with it. If you are fine with giving up the drinking in the short term, it will be much easier to do so and get through your probation without a hitch.
Don't push your luck. Clean up because you will be tested at random. I was a Dallas County Probation Officer in the 90's and I would sometimes test people more than once in a week just to see if they would be using a day or so after a drug test.
Just follow your conditions and they are required of you and you'll be fine. Give them nothing to work with and they won't be able to violate you. Mess up and you will be potentially facing up to 180 days for a first offense DWI. Up to a year if your DWI was enhanced to a higher level due to the amount of alcohol in your system at the time of your arrest.