His La crocifissione premièred at La Scala in 1954 to great acclaim. 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).
