acid test vs verification

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"). 

verification

noun
  • The act of verifying. 

  • The state of being verified. 

  • Confirmation; authentication. 

  • A formal phrase used in concluding a plea, to denote confirmation by evidence. 

  • The operation of testing the equation of a problem, to see whether it truly expresses the conditions of the problem. 

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