acid test

From the testing of gold with nitric acid (true gold is not affected).

acid test (plural acid tests)

1. (figuratively) A rigorous test or appraisal of the quality or worth of something.
   • 2020 May 20, Stefanie Foster, “Comment: Safety first: now more than ever”, in Rail, page 3:

     The acid test: will the British public abide by such stringent guidelines about where they should stand, walk or sit in our stations and on our trains, when they have been used to a turn-up-and-go railway where they enjoyed freedom having bought their ticket?

   • 2021 July 7, Phil McNulty, “England 2-1 Denmark”, in BBC Sport‎:

     This was the acid test - at least before Sunday's final with formidable Italy - and they came up with the goods not only in the context of Euro 2020 but also in demonstrating their character and big match mentality.

2. (historical) In the 1960s, a party based around the use and advocacy of the psychedelic drug LSD ("acid").

• “acid test”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.

• dictates, testacid