Co je attest? Co je attest? To affirm to be correct, true, or genuine: The date of the painting was attested by the appraiser. To certify by signature or oath: attest a will. To certify in an official capacity. To supply or be evidence of: Her fine work attests her ability. See Synonyms at indicate.To put under oath.To bear witness; give testimony: attested to their good faith. Archaic Attestation.