litmus test
noun [ C ] uk/ˈlɪt.məs ˌtest/ us/ˈlɪt.məs ˌtest/
石蕊测试，酸碱测试
a test to find out if a substance is acid or alkaline
[ usually singular ]（具有更广泛意义的）决定，意见
someone's decision or opinion about something that suggests what they think about a wider range of related things
The president's policy on abortion is regarded as a litmus test of his views on women's rights. 总统在堕胎问题上所采取的政策表明他对女性权利的总体看法。