Tests have long been the main methods to evaluate students' knowledge, skills and development. Besides providing assessment results, tests also cause test anxiety in students - a phenomenon that has recently attracted the attention of many scientists, researchers and scholars worldwide.This article aims to summarize researchers' definitions, classifications, and discussions of this phenomenon in order to present a picture that reflects the problem in different teaching contexts. In addition, ways to measure test anxiety levels are also provided to help readers, especially students, have tools to understand their inner state when taking the tests.The findings from this study will benefit not only researchers and teachers interested in the same topic by providing thorough background information on test anxiety, but also beneficial for students who need to quantify their anxiety levels during tests.