I don’t practice in McAllen, but I’d be pretty surprised if any/every county in Texas didn’t require submission to random U/As, especially on an alcohol or drug related case, as a condition of probation.
From a practical standpoint, you’ve already taken the U/A, and since use of (alcohol/marijuana/cocaine/illegal substances) is almost certainly a violation of your probation, even if U/As aren’t, the ship may have already sailed for you.
Still, it’s an interesting hypothetical (since I’m assuming that random U/As are required but that you didn’t know that): whether or not a “forced” U/A when it wasn’t specifically a condition of probation would be admissible against you in a probation revocation proceeding.
Make sure you catch up on payments, community service, and all other potential areas for violation, and get yourself a good lawyer.
I'd agree with Jamie's take. Even if random UAs are not specifically part of your probation, there's probably some condition in there about "do not violate any laws of the State of Texas". Taking any sort of illegal drugs is obviously against the law (since it requires you to possess them, even if just for a fleeting moment) and your PO will likely be upset.
What can happen is your probation CAN be revoked for this, but only a lawyer more familiar with your case, your court, and your probation department can tell you what WILL (or is likely to) happen. Talk to the lawyer that put you on probation or another local criminal defense attorney ASAP.
Disclaimer: This answer is provided as a public service and as a general response to a general question, it is not meant, and should not be relied upon as specific legal advice, nor does it create an attorney-client relationship.
I agree with the assessments of both of my colleagues. Random drug testing is a typical condition of probation throughout the country; just as not committing another crime is. If you think you failed because you were using drugs, consult with that lawyer about coming clean with your PO. Good luck.
Since I do not practice law in your State, this answer is provided solely for informational purposes only, for you to use as a starting point when speaking directly with a lawyer in your State. This answer does not constitute legal advice, create an attorney-client relationship, or constitute attorney advertising. I urge you to immediately contact an experienced criminal defense lawyer admitted to practice law in your State before you make any decisions about this case.