1590s, "bear witness to, officially confirm; give proof or evidence of," from 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.
<a href="https://www.etymonline.com/word/Attested">Etymology of Attested by etymonline</a>
Harper, D. (n.d.). Etymology of Attested. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/Attested