The popularity of diet fads is a 'testimony to' the fact that people want a quick fix for their health and weight problems.
It is 'testimony to' her courage and persistence that she worked for so long in the face of such adversity.
There were contradictions in her 'testimony'.
(..) do you have any proof of what you're saying? Ask Agathe. She rescued me. GASTON: (LAUGHING) Agathe! You'd hang your accusations on the testimony... of a filthy hag? No offense, Agathe. Monsieur LeFou. He was there. He saw it all. Me? (..)2017 Beauty and the Beast