In California unless there is affixed to your parole papers a "8B" condition, which is totally abstaining from alcohol, you probably can drink and even if you test "dirty" this should not be a parole violation. However, if the use of alcohol is also involved in a crime, such as driving drunk or being drunk in public (647f Penal Code) your parole can be revoked but only because the drinking was incidental to the arrest for something else.  In other words, unless there is a written condition saying you can't drink anything, you should be able to have a drink or two or three and this is not a violation of the terms of your parole. After all, it is not illegal to sociably drink alcohol.

Under Morrissey v. Brewer, a United States Supreme Court case, you have substantial "due process" rights if you plead not guilty to a parole violation.  However, if you lose at the hearing you could be subjected to up to a year in prison for the violation, or about 9 months for good behavior. The way California's parole violation procedure is that if you  are accused of being in violation of the terms of your parole and this means you'll probably be sent to jail with a "no bail" hold because technically you are still in custody.  The parole agent will "suggest" you plead guilty and, depending on the violation, he'll try to "plea bargain" your case and if the violation isn't serious, e.g., a minor technical violation of the rules, you'll probably only do about two months.

As for testing your blood alcohol content, this will be done at the parole office or in the "streets" with portable alcohol screening devise (PAC). Or the test will probably be a breath test at the police station where it can be administered and the result will appear immediately.

I hope this information is helpful to you.  The parole agents have much power, so it isn't a good idea to argue with them. With the parole people, in order to get along, you have to go along with their technical violations of their rules.  They can have you arrested for almost any reason, or there will be a "pretext" reason to form of the basis of the violation.