Alcohol is metabolized before it is eliminated, which means that alcohol itself doesn't show up in urine tests. Instead, ethyl glucoronide (EtG), which is a direct metabolite of alcohol, is the substance being tested for in alcohol tests. It is detectable in urine 3-4 days, or about 80 hours, after ingesting alcohol. For more information on alcohol testing, you can read here: http://www.drugtestingnetwork.com/alcohol-testing.htm
Alcohol break down in the body makes it difficult to detect through urine. It is detected through blood alcohol level more accurately. If they are testing for drugs, yes, alcohol is one of the default markers.
Alcohol tests are performed at jobs and as part of law enforcement procedures. Breathalyzers, blood, and urine tests are the methods used. Urine tests can test positive up to three to four days depending on the individual and how much alcohol was ingested.