a litmus test meaning in English

[网络] 检验标准

marked by a different degree of intensity in different regions, infectious diseases, working as a litmus test, expose social and economic problems, aggravate social inequality and contribute to discrimination
双方高度重视在打击非法移民领域的合作。根据两国元首达成的协议，双方正加紧筹备成立中俄移民问题联合工作小组。
translate the following sentence into chinese, ‘ text messaging, or sending 160 characters of fewer to another cell phone, has become a discreet way to contact someone and, because it takes some tech-savvy know-how, it's a litmus test of sorts on how advanced a nation is in using wireless technology
发送文本信息,或者说发送少于160个字到另一部手机已成为联系别人的一种隐秘的方法.因为这需要一定的技术技能,也就成为了一个国家在使用无线科技先进程度的试金石