Fig.: a particularly difficult situation which will either prove or disprove the worth of someone/something

7'4" is not an out-of-reach measure for a high jumper, but it's an acid test for athletes who are in shape

2,20 metri non è una quota proibitiva per un saltatore in alto, ma è già un banco di prova per la forma degli atleti

That terrible dirt road on the mountain, with ice and snow, will be the crucial test for our new jeep

Quel terribile sterrato in montagna, con ghiaccio e neve, sarà la prova del fuoco per la nostra nuova jeep

They say that the soccer player has fully recovered from his knee injury, and the next match will be his acid test

Dicono che il calciatore si sia completamente ripreso dall'incidente al ginocchio, e la prossima partita sarà la prova del nove

The "acid test" was a test used by jewelers and chemists to prove gold from other metals. Since concentrated nitric acid does not dissolve gold, but it will dissolve other base metals or alloys, such as brass, when a jeweler was offered gold, he would give it the acid test by placing a drop of nitric acid on it to see what happened