The phrase "attested by many" is correct and usable in written English.
It can be used when referring to something that has been confirmed or supported by a number of people or sources.
Example: "The theory of climate change is attested by many scientists around the world."
Alternatives: "supported by many" or "verified by numerous".
The success of this universal creed can be attested by many innovations of recent decades that now look perfectly natural.
The functions of the drugs as teachers, leading participants through experiences of spiritual growth, are attested by many members of contemporary drug cults.
The scour depth greater than 2 m were also attested by many road failures found in south Lhok Nga, Indonesia Pariss et al., 2009) and Kamala, Phuket, Thailand (Lukkunaprasit and Ruangrassamee, 2008) during the 2004 Indian ocean tsunami.
As attested by many chronicles, it was the principal form of organization governing land ownership in the 13th century.
Many writers, including notably Ogden Nash, have parodied Kilmer's work and style as attested by the many parodies of "Trees".
This is attested by Daniel Sennert and by many hitherto little-known French and English natural philosophers.
Armagh's prosperity in the 18th century is attested to by many monuments and buildings.
Although the authenticity of his age was attested to by many persons, including two celebrated Scandinavian actuaries, later investigations cast doubt upon the record.
When he was a youngster, his musical idols were trumpeters -- his cousin Theodore (Cuban) Bennett, who never recorded but whose advanced musical ideas were attested to by many musicians, and Bubber Miley, a star of Duke Ellington's orchestra in the late 1920's who lived around the corner.
That Shingle Street represents a climate change that's bodily as well as global is attested by the presence of many short lyrics haunted by mortality.
The continuing vitality of the religious system he founded in the 13th century is attested by the fact that many of the modern Buddhist sects now flourishing in Japan are, in various degrees, based on Nichiren's doctrines.
