attestation vs testimonial

attestation

noun
  • A thing that serves to bear witness, confirm, or authenticate; validation, verification, documentation. 

  • The process, performed by accountants or auditors, of providing independent opinion on published financial and other business information of a business, public agency, or other organization. 

  • A confirmation or authentication. 

  • An appearance in print or otherwise recorded on a permanent medium. 

testimonial

noun
  • A statement, especially one given under oath; testimony 

  • A match played in tribute to a particular player (who sometimes receives a proportion of the gate money). 

  • A tribute given in appreciation of someone's service etc. 

  • A written recommendation of someone's worth or character 

adj
  • Serving as testimony. 

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