"was attested" is correct and usable in written English.
You can use it when you are trying to provide evidence that something is true. For example, "The authenticity of the document was attested to by two eyewitnesses."
The quality of the process was attested by Young's modulus and electrical conductivity measurements.
That was attested to by CNN closing down its Afghanistan operation this week.
Therese Neumann's capacity for inedia was attested to by four Franciscan nuns, who attended her in rotating shifts in 1927.
Jamal's musical fertility was attested to by both his playing and the number of new originals he introduced.
Efficient knockdown of Orai3 during EACH was attested at the mRNA and protein levels (Fig. 8D,E).
The applicability of method was attested by analysis of water samples yielding good recovery values (91.4 103.5%).
By the 12th century, according to the chronicles, the city's wealth and religious importance was attested to by its more than 400 churches.
Its influence was attested by the recognition of July 27, the date of the church's formal establishment, as a Philippine national holiday in 2009.
The supporters of what would become orthodox Christianity stressed the need to adhere to tradition, which was attested by the churches of apostolic foundation.
The obtained copolymer-grafted MSNs (copoly-MSNs) were physico-chemically characterized and their biocompatibility was attested on a human keratinocyte cell line (HaCaT).
By increasing agricultural output, he was able to compound tax revenues, the success of which was attested to by the treasury surplus that remained upon his death.
