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'.
(..) you didn't hear them? No, I didn't. You didn't, huh? What I'm saying is... The tutor came and revoked her testimony. She says you knew. - She said I knew? - Yes, she came yesterday. He threatened her... Answer me. (..)2011 A Separation