prep vs test flight

prep

noun
  • Preparation. 

  • A student or graduate of a prep school, a preppy. 

  • A prep school. 

  • preparatory level; the last two levels or the fourth and fifth years of preschool; the two levels before first grade. 

  • Homework, work set to do outside class time, used widely in public schools and preparatory schools but not state schools. 

verb
  • To prepare. 

test flight

noun
  • a proving flight; usually of a prototype of a new aircraft design before it goes into production. 

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