How would you normally format a testimonial?

Find out who you are writing to, if you don’t know. To whom it may concern is fine. Just say right away who you are and in what regards you are writing for.

Dear Sir or Madam or To Whom it May Concern (I just double-checked the capitalization protocol) covers all your bases regardless of the recipient. The reader isn’t going to be as concerned with the address as he/she is with the content.

Thanks! All done and sent off. I just wasn’t sure.

Hurray! Something off the to-do list… celebrate with wine!

Lol, later maybe. Still working. Thanks for your help @whitetigress and you my friend @Blueroses.

@Bellatrix I’ve arrived late once again and I don’t know if I could have helped you but you’ve sent your testimonial off, so it’s moot anyway, so… all that is left to do is to congratulate you for doing so and for striking yet another item off your to-do list! Yay, Bellatrix!