Verb (used with object) : to attest the truth of a statement. ,His works attest his industry.    From Dictionary.com. 

Verb (used without object) : to attest to the reliability of an employee.    From Dictionary.com. 

I cannot summon Carwin to my bar, and make him the attestor of my innocence, and the accuser of himself.    From Wordnik.com.  [Wieland: or, the Transformation, an American Tale] Reference

It was said that an attestor had been called Cicero from "cicer," a vetch, because his nose was marked with the figure of that vegetable.    From Wordnik.com.  [Life of Cicero Volume One] Reference

It was said that an attestor had been called Cicero from “cicer,” a vetch, because his nose was marked with the figure of that vegetable.    From Wordnik.com.  [The Life of Cicero]

This arch attestor for the public good 640.    From Wordnik.com.  [The Poetical Works of John Dryden, Volume 1 With Life, Critical Dissertation, and Explanatory Notes] Reference