specimen vs test piece

specimen

noun
  • An eligible man. 

  • An individual instance that represents a class; an example. 

  • A banknote printed for distribution to central banks to aid in the recognition of banknotes from a country other than their own 

  • A sample, especially one used for diagnostic analysis. 

  • A postage stamp sent to postmasters and postal administrations so that they are able to identify valid stamps and to avoid forgeries 

test piece

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