I think there are two meanings. One comes from Database Theory, and I'm not sure if the other one comes from that, or from a chemical test used with silver, but here are the two meanings: 1. From Database Theory, ACID is an acronym meaning Atomicity (Either everything commits, or nothing commits), Consistency (Everybody sees the same thing), Isolation (Nobody can do an operation that messes up another operation) and Durability (once the transaction commits, then it is always committed, even in the event of failure). In this sense, it is the definition of a transaction. It is a test of reliability of a transaction. 2. Acid test can also come from a test used to detect fakes of silver. With this test, nitric acid is applied to the silver. Silver will not corrode with nitric acid, but the common fakes for silver that were passed off to tourists would quickly react with the nitric acid and corrode. This made a fake readily apparent. From this sense, the acid test refers metaphorically to any test that readily makes a fake apparent. If it stands up to the acid test, then it is genuine. Hopefully, that makes sense of the two ways I see it used. The second sense is probably what you are seeing used.

The idiomatic meaning is a test which will really prove the value, quality, or truth of something. For example: 1) The new TV show was well received but viewing figures for the next episode will be the real acid test. 2) The acid test for the product will be whether people actually buy it. 3) The play passed the critic's acid test.

As a cultural side note, one that is probably unrelated to the use of acid test as you are reading it: the Acid Tests were also several events/parties hosted by Ken Kesey, the author of One Flew Over the Cuckoo's Nest, and his friends, the Merry Pranksters, in the San Francisco area. These parties took place in the mid-sixties when LSD, also known as acid, was still legal, and very few people had taken the drug. Posters and handbills would announce the event saying, "Can you pass the acid test." Large quantities of the drug were consumed at each party. People got weird. The house band would later become The Grateful Dead. Here's a poster: http://www.postertrip.com/public/images/5594a.jpg Here's a video: http://www.youtube.com/watch?v=j3XA4KSdKWM Here's a book: http://www.jellojello.com/temp/The%20Electric%20Kool-Aid%20Acid%20Test.pdf These parties mark the beginning of the Haight/Ashbury scene (a neighborhood in San Francisco that became the epicenter of the hippie movement) and the hippie movement itself.