at·test / əˈtest/ • v. [tr.] provide or serve as clear evidence of: his status is attested by his recent promotion | [intr.] his numerous drawings of ships attest to his fascination with them. ∎  [intr.] declare that something exists or is the case: I can attest to his tremendous energy the deceased's attorney attested that he had been about to institute divorce proceedings. ∎  be a witness to; certify formally: the witnesses must attest and sign the will in the testator's presence.DERIVATIVES: at·tes·ta·tion / ˌateˈstāshən/ n.

attest XVI. — F. attester — L. attestārī, f. AT- + testārī witness (cf. TESTAMENT).
So attestation XV.

ATTEST

To solemnly declare verbally or in writing that a particular document or testimony about an event is a true and accurate representation of the facts; to bear witness to. To formally certify by a signature that the signer has been present at the execution of a particular writing so as to rebut any potential challenges to its authenticity.