I'm not sure who he replaced as capo, but I'm under the impression that went Scarfo went to the can for the weapons charges in the early 80's, Chuckie Merlino was running things on the street and Testa was bumped up to acting underboss at the time to help Chuckie run things in South Philly.

Supposedly, Leonetti says in his book that he was running things in Atlantic City at the time too while Nicky was away.

When Testa was bumped up, Tommy Del and Faffy Iannarella ran the crew together. Then, when Ciancaglini Sr. was arrested, Tommy Del and Faffy were both bumped up to acting capo's to fill Testa and Ciancaglini's spots, respectively.