свидетельствовать о(The growth of high technology in Massachusetts is testimony to the incredible potential of the technological innovator – Small Business Innovation Research Act of 1981 Tamerlane)
являться свидетельством(This fact bears testimony to the special attractiveness of Devonport and the efficiency and cheapness of the ferry service – New Zealand HeraldTamerlane)
являться свидетельством(... and the fact that this was ultimately accomplished stands as testimony to the success of their efforts – by Ed MickolusTamerlane)