attest (v.)

1590s, "bear witness to, officially confirm; give proof or evidence of," from Middle French attester (Old French atester, 13c.) "affirm, bear witness to," from Latin attestari "confirm, prove," literally "bear witness to," from assimilated form of ad "to" (see ad-) + testari "bear witness," from testis "witness" (see testament). Related: Attested; attesting.