Hézuò zhōng zuì néng kàn qīng yīgè rén, nà shì yǒuyì de shìjīnshí.
Working together reveals people like nothing else - it's friendship's true touchstone.
Tips
culture
Originally a real object: a black siliceous stone against which jewellers rubbed gold to judge its purity by the streak it left. The figurative 'reliable test' sense tracks the Western use of 'touchstone' exactly.
