pop quiz vs probation

pop quiz

noun
  • A quiz or test given without warning or prior announcement. 

probation

noun
  • A testing period of time 

  • A period of time when a person occupies a position only conditionally and may easily be removed for poor performance 

  • A type of sentence where convicted criminals are allowed to continue living in the community but will automatically be sent to jail if they violate certain conditions 

How often have the words pop quiz and probation occurred in a corpus of books? (source: Google Ngram Viewer )