The phrase "acid test" means a situation or test that reveals the true nature or quality of something or someone, usually under difficult or challenging conditions. Full definition
We can often detect nutrient deficiencies via lab tests, such as a urine organic acids test for some B vitamins. (mommypotamus.com)
It's recommended you have another bile acid test done after four months to check on your dog's surgery status. (animalbehaviorcollege.com)
The lesson leads on to a bumper worksheet where students need to calculate and analyse current ratios and acid test ratios for a number of businesses. (tes.com)