acid test vs examination

acid test

noun
  • A rigorous test or appraisal of the quality or worth of something. 

  • In the 1960s, a party based around the use and advocacy of the psychedelic drug LSD ("acid"). 

examination

noun
  • The act of examining. 

  • Interrogation, particularly by a lawyer in court or during discovery. 

  • Particularly, an inspection by a medical professional to establish the extent and nature of any sickness or injury. 

  • A formal test involving answering written or oral questions under a time constraint and usually without access to textbooks; typically, a large, written test administered to high school and college students covering course material studied in a semester. 

How often have the words acid test and examination occurred in a corpus of books? (source: Google Ngram Viewer )