acid test

the acid test (a very thorough test: a fact, event, or situation that proves something, for example whether a plan will work; a test whose findings are beyond doubt or dispute, something that proves whether something is good, effective, etc, or not) — серьезное испытание, решающая проверка

put sth through the acid test, give sth the acid test — подвергнуть серьезной проверке

Example 1: We put your invention through the acid test, and—I am extremely sorry to tell you—it failed miserably. (thefreedictionary.com)

Example 2: I’ll take this home to my kids and let them give it the acid test. If it survives them, it’s a winner. (thefreedictionary.com)

Example 3: Her new husband seems generous, but the acid test will be if he lets her mother stay with them. (thefreedictionary.com)

Example 4: The senator doesn’t look too popular just now, but the acid test will be if he gets reelected. (thefreedictionary.com)

Example 5: The state of the economy is usually the acid test of any government's success. (MM)

Related vocabulary:
[litmus test]
analysis, conclusive test, critical test, crucial test, decisive test, definitive test,
experiment, proof, proving ground, substantiation, sure test, trial, verification
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Origin
The phrase is derived from a test for determining true gold using acid: gold is the only metal not to dissolve in many types of acid. Thus, dipping a piece of metal of unknown origin into acid is an acid test of whether it is gold.