the beer is gone by then. if it's like a probation situation, they test for something in urine your body gives off from processing alcohol. they claim they can detect 48 hrs.
"Ethyl glucuronide (EtG) is a direct metabolite of alcohol (ethanol). Its presence in urine may be used to detect recent ethanol ingestion, even after ethanol is no longer measurable. The presence of EtG in urine is an indicator that ethanol was ingested and can be detected in urine for up to 80 hours after ingestion."
If your on probation, then supposedly they can detect for 3 days, though that's generally with heavy drinkers. Not worth the risk IMO.