Attest (verb)

1. To provide evidence or proof of the truth or validity of something.
2. To affirm or declare to be true, genuine or accurate.
3. To act as a witness or to give testimony to support something.

Origin:

From the latin word 'attestari' meaning to bear witness, certify or confirm.

Examples:

1. The document was attested by a notary public.
2. The scientist attested to the accuracy of the experiment's results.
3. The testimonials attested to the effectiveness of the new product.
4. The employee attested to the truth of the statement under penalty of perjury.
5. The survivor attested to the horrors of the war in her testimony to the court.