He studied with Giulio Cesare Gedda and Luigi Perrachio at the Turin Conservatory, and took an arts degree at Milan University (1951).
The expressiveness of work was particularly admired and the composer followed similar style in his Stabat mater (1957) and New York oficina y denuncia (1964), the latter of which denounced the dehumanizing environment of the modern metropolis.
The work coincided with the Testi's conversion to the Marxism, and was followed by other compositions highlighting social and political concerns, including the Neruda setting Canto a las madres de los milicianos muertos (1967) and Cori di Santiago (1975).
L’albergo dei poveri (1966) displays a clearly characteristic attitude of rough dramatic purpose, confirmed in Il sosia (1981) and Riccardo III (La Scala, 1987), works which probe intensely into the psychology of their characters.
In general Testi's style, rather than adhering to the radicalisms of the post-Webern avant garde, re-elaborates and reflects, not without eclecticism, certain crucial 20th-century achievements, from Stravinsky and Bartók to early Schoenberg.