The phrase "attest not only" is correct and usable in written English.
It can be used when you want to indicate that something confirms or verifies more than one aspect or point.
Example: "The results of the study attest not only to the effectiveness of the treatment but also to its safety."
Alternatives: "confirm not only" or "verify not only".
As a former student of Professor Johnson, I wish to take this opportunity to attest not only to her intellectual rigor but also her fidelity to the church.
He can attest not only to the quandary of a field officer directed to take extreme measures, but also to the personal cost that can follow.
The wall texts, the new catalog and especially the descriptive captions attest not only to a shift from artifice to authenticity in public taste but also to a greater measure of truth-telling about museum policies.
This elegantly assembled creation vies with the salmon and with a fricassee of black cod and lobster in a sweet, creamy, cumin-seasoned sauce for the honor of best entree, and all three dishes attest not only to Mr. Nish's good judgment but also to the kitchen's steadiness.
His tale and the myriad other plot lines it generates attest not only to Mr. Wagner's range as a writer -- his ability to write with affecting sincerity as well as satiric glee -- but also to his power as a storyteller to beguile.
This attests not only to the scale of the farm but also for their need for adequate irrigation.
This attests not only to the undiminished attraction of the American system but also to a sea-change in popular attitudes toward the United States.
It has attested not only to the machines' accessibility, but also to their security and accuracy -- neither of which is within the federation's areas of expertise.
It attests not only to his own remarkable talents but also to a personal courage that he shares with other cancer survivors.
Security of overlay networks requires that the integrity of the software stack of a node is attested not only when a node joins an overlay but continuously, to discover updates of its configuration due to malware.
Christianity became established in the 2nd century, and the extent of its organization is attested not only by accounts of martyrdoms during the 3rd century but also by the records of one of the earliest councils at Elvira, about 306.
