Robbie co-wrote Sweet Fire of Love with U2 and they are his backing band for the track. On vocals it's a Bono and Robbie duet. Daniel Lanois, who produced the album with Robbie, is credited with background vocals as well as percussion. My CD booklet credits both Adam and Bono on bass, which I think must have been a misprint because I'd never heard of Bono playing bass before. It's a beautiful track, one of my very favorite "unofficial" U2 songs. And yes, it does sound like a JT outtake.
Testimony was written by Robbie solo. U2 is the backing band once again, but Bono's vocal is basically just a backing vocal. I like this song too, but not nearly as much as "Sweet Fire of Love."
The whole CD is great.