Poetically, alongside Gabriello Chiabrera, he was the major exponent of the Hellenizing strand of Baroque classicism, combining Horatianism with the imitation of Anacreon and Pindar.

His first volume of verses, published at Venice in 1613 and dedicated to his patron and lord Alfonso III d'Este, followed the well-established vein of the Baroque pastoral idyll and courtly Mannerist marinismo.

His Rime published in 1617, anticipated by their dedication to Carlo Emanuele, Duke of Savoy, the anti-Spanish octaves they contained, which were composed in 1615 and better known under the title Il pianto d'Italia,[2] and characterized the injuries being suffered by the Spanish hegemony in Italy, to such a degree that the Spanish Resident at the Duchy of Modena tendered a remonstrance, in consequence of which the printer Giuliano Cassiani was arrested and the edition suppressed.

Henceforth, Testi's career took him on a long series of travels of a diplomatic nature, notably to Vienna, Rome, Venice and Turin, with the result that in April 1635 he was awarded a feudal demesne that brought him the title of conte At the end of that year he was sent as ambassador to the court of Spain.

Embarking 10 March 1636 at Vado, where he encountered an old acquaintance from Rome, Gabriello Chiabrera, his embassy in Madrid, which brought him the cross of the Order of Santiago, lasted exactly a year, though he would be sent again in 1638.