"testimonial letter" is correct and usable in written English.
You can use it when referring to a letter written in support or praise of someone or something, such as when asking for a reference from a former employer. For example, "I included a testimonial letter from my former supervisor as part of my job application."
The other day, Charlie Watts ("the drummer from the Rolling Stones," said his testimonial letter on the wall) was due to drop by for a fitting.
At the Saturday evening performance, Mr. Foss's two decades' service were acknowledged, and he was given a testimonial letter from President Bush.
Cole Porter rather cherishes the idea of himself as a small-town boy, and he will sometimes ingenuously show visitors at his apartment the testimonial letter and bronze medal presented to him two years ago by the town of Peru, Indiana, in whose environs he was born.
Presidential hopeful Carly Fiorina, the fired Hewlett Packard executive who it seems mistook her golden parachute for a testimonial letter, called Cook a hypocrite for doing business in oppressive countries.
Also ask them to write you a testimonial letter.
For example, if you sold a teeth whitening product that takes up to 3 months to work efficiently, send your customer the testimonial letter after 3 months have passed so they can provide an appropriate testimonial.
The Burberry diaspora, as evoked by testimonial letters sent to the company, mirrored Britain's: Salonika, Ceylon, Burma, Formosa, Constantinople, Borneo, the Orange Free State.
The school also sent home a sort of yearbook, long obsolete in most no-frills poorer elementary schools, full of photographs of students, samples of their work and testimonial letters from parents.
So after eliciting testimonial letters from the lord mayor of Dublin and the Irish consulate cultural attaché in New York, and after reading that pleading letter to the mayor, Adrian Benepe, the parks commissioner, gave the project the go-ahead and even found a way to reduce the rental costs.
After his arrest, a number of people in Benicia — an antique dealer, a hot-dog vender, an artist, an ex-junkie — wrote testimonial letters in support of his fine character; and for a time "Free New York Frankie" T-shirts were sold and worn in the town.
Snoopy is nominated for the Daisy Hill Puppy Cup and proceeds to bully and blackmail the neighborhood kids into writing testimonial letters for him.
