What is the limitus test?

A litmus test is a simple method used to determine the acidity or alkalinity of a solution, typically involving a dye derived from lichens. When a litmus paper strip is dipped into a solution, it changes color based on the pH level: red indicates acidic conditions (pH less than 7), while blue indicates alkaline conditions (pH greater than 7). Beyond its chemical use, the term "litmus test" is also commonly used metaphorically to describe a definitive criterion or test for judging something.