Pietro Testa was Barzini family's senior caporegime and most trusted caporegime, and Consigliere of Mariposa crime family. In 1936 he, along with a Barzini Capo was tasked with murdering Corleone Soldato Johnny Trapani.
Murder of Johnny Trapani
In early 1936, Pietro and a capo blew up Johnny Trapani's bakery in Little Italy. In the ensuing chaos, a group of Barzini hitmen grabbed Corleone Soldato Johnny Trapani and dragged him into the back alley. Despite being outnumbered, Trapani managed to fend them off but was cornered upon exiting the alley by the two capos and their boss Emilio Barzini himself. Knowing it was futile to attempt an escape, Trapani stood still while the capos riddled him with Tommy Gun bullets.
After the execution, Johnny's twelve year-old son Aldo stumbled upon his body alongside Vito Corleone and a group of bystanders. Vito Corleone stopped the young boy from seeing his father's corpse, and promised that when the time was right, he could take his revenge.
In 1951 Aldo, now a full grown man and made man in the Corleone family, was tasked by Al Neri to assassinate Testa. He was causing trouble by making a deal with the Little Italy Police Chief, and therefore turning the police force against the Corleones.
Aldo arrived at the meeting, which took place under an overpass in Little Italy. After watching over the meet for a few minutes, he waited until Testa and the chief shook hands, then shot Testa in the head, killing him instantly.