He studied under Simon Vouet and became a friend of Charles Le Brun, who was working in the same studio. According to a biography edited by Georges Guillet de Saint-George, Testelin and Le Brun collaborated "on some paintings and decorative schemes" for the former church of Val-de-Grâce. He also painted the Mays for 1652 (Saint Peter Reviving the Widow Tabitha, now in the Musée des beaux-arts d'Arras) and 1655 (The Whipping of Saints Paul and Silas).
