"attest in" is a grammatically correct phrase and is commonly used in written English.
It means to bear witness or provide evidence for something. Example: The signatures of the witnesses attest to the authenticity of the contract.
"Something inside is happening again," the anonymous composers attest in the intoxication that preceded their fate.
Having gone through that experience, I can attest, in a non-masochistic way, that pain is a great teacher.
Speak we must, of course, as both sisters attest in one of the dense, musical monologues that they recite in turn.
Living organisms are reliably, inspiringly unpredictable, as any birdwatcher can attest; in years of watching, we have seen many species only once, so it is very likely we have missed many more.
And as Jeremy Bedzow, an M.B.A. student at the IE University in Madrid, can attest, in business school it often pays to volunteer — especially if you are looking for rewards that go beyond the bottom line.
Christmas may be an entire time of year, but it all comes down to the one day in the calendar when many of us attest in our own ways to the solemn, joyous miracle of our lives.
In addition, a number of Median personal names are attested in various sources.
An early form of Canaanite is attested in the Tell el-Amarna letters (c. 1400 bc).
By some means, however, the tribe as such survived and is attested in imperial times.
The earliest Tamil writing is attested in inscriptions and potsherds from the 5th century bce.
This use of these three preterit forms is also attested in narrations in later Vedic texts.
