provide evidence for; stand as proof of; show by one's behavior, attitude, or external attributes
"His high fever attested to his illness"
"The buildings in Rome manifest a high level of architectural sophistication"
"This decision demonstrates his sense of fairness"
authenticate, affirm to be true, genuine, or correct, as in an official capacity
"I attest this signature"
give testimony in a court of law
"The witness stepped forward to attest that she saw the defendant leave the scene before the police arrived."
To affirm to be correct, true, or genuine.
"The old family heirloom attests to our ancestors' humble beginnings in this very town."