Attest

to bear witness to; certify; declare to be correct, true, or genuine; declare the truth of, in words or writing, especially affirm in an official capacity:
to attest the truth of a statement.
to give proof or evidence of; manifest:
his works attest his industry.
to put on oath.
to testify or bear witness (often followed by to):
to attest to the reliability of an employee.
archaic. witness; testimony; .
contemporary examples

survivors of ebola, as thousands in west africa can attest to, can—and often do—make a full recovery.
the sham, scaremongering guide to ebola abby haglage november 19, 2014

anyone familiar with the events of four years ago can attest to that.
the decision 2: lebron james trolls the world… again marlow stern july 10, 2014

as a native jersey boy, i can attest that our storage facilities are vast.
america’s public library crisis: who’s reading the books? jon reiner may 22, 2012

any white person who has traveled in rural asia or africa can attest to the discomfort of sticking out as the only caucasian.
even if racism abates, its effects don’t megan mcardle may 30, 2013

as sarah palin can attest, republicans long ago sacrificed the vice-presidential slot to the propaganda of speed.
chris christie and the runaway high-speed presidency train james poulos january 10, 2014

historical examples

this is another of the accidental coincidences which attest the genuineness of the acts.
the expositor’s bible: the acts of the apostles, vol. 2 g. t. stokes

nor is there any year of his life when his work does not attest a clear eye and a firm hand.
holbein beatrice fortescue

if the letter was preserved the seal was kept attached to it in order to attest its authenticity.
the private life of the romans harold whetstone johnston

all attest that in dreamland there is no such thing as repose.
the world i live in helen keller

and as to durability, let the cloak of kalaalaneo, now several centuries old, attest.
hawaiian folk tales various

verb
(transitive) to affirm the correctness or truth of
when intr, usually foll by to. to witness (an act, event, etc) or bear witness to (an act, event, etc) as by signature or oath
(transitive) to make evident; demonstrate: his life of luxury attests his wealth
(transitive) to provide evidence for: the marks in the ground attested the presence of a fossil
v.

1590s, from middle french attester (old french atester, 13c.) “affirm, attest,” from latin attestari “confirm,” literally “bear witness to,” from ad- “to” (see ad-) + testari “bear witness,” from testis “witness” (see testament). related: attested; attesting.