Acid test

a severe and conclusive test to establish quality, genuineness, worth, etc.
Contemporary Examples

The debt ceiling vote will be something close to an acid test that this budget deal represents a cease fire in the budget wars.
Republicans Compromise on the Budget, but Don’t Expect Them To Compromise on the Debt Ceiling Eleanor Clift December 17, 2013

In his new book acid test, author Tom Shroder tells the story of Nick, a veteran haunted by PTSD.
Psychedelics Are Ready for a Comeback Abby Haglage September 7, 2014

It may be painful, but this is an acid test for Republicans.
Obama Realigns, the GOP Declines: The New Political Paradigm Robert Shrum January 31, 2013

Historical Examples

The acid test of any service done for our soldiers in France is the value the men themselves place upon it.
The War Romance of the Salvation Army Evangeline Booth and Grace Livingston Hill

I have submitted that water-district plan to the acid test, Colonel.
The Landloper Holman Day

The writer believes for city milk inspectors that the acid test would serve a very useful purpose.
Outlines of Dairy Bacteriology, 8th edition H. L. Russell

He handled the Sunday excursions, which was the acid test of a trainmans grit.
Local Color Irvin S. Cobb

On the whole Buck Weaver would stand the acid test, the old soldier was coming to think.
Mavericks William MacLeod Raine

Like the dying––or the reborn––Northrup put his loved ones to the acid test.
At the Crossroads Harriet T. Comstock

The acid test in arithmetic was not the mastery of the method, but the number of minutes required to work out an example.
The Americanization of Edward Bok Edward William Bok

noun
a rigorous and conclusive test to establish worth or value: the play passed the critic’s acid test

noun phrase

A party at which LSD is added to food and drink

verb phrase

To provide special effects at a party, usually of a psychedelic sort: He acid-tested his place with colored strobe lights

[Narcotics; punning adaptation of ”a final and decisive test”]
A decisive trial to determine worth or quality, as in Exposure to brilliant sunlight is the acid test for showing this fabric won’t fade. Alluding to a 19th-century chemical test for distinguishing gold from other metals, this term was used figuratively by the early 1900s.