Mancuso, who had served time for murder, pulled a knife. Testa, 77, a retired hospital security guard - and a well-liked man, his neighbors said - stepped between the men.
But he quickly stumbled back inside and collapsed to the floor.
"Ro, he stabbed me three times. Hurry up and get a towel," he told his sister Rose Knowles, 80, whom he lived with.
Testa died at the Hospital of the University of Pennsylvania at 49 minutes past midnight, one of six people killed in the city between Saturday afternoon and Sunday morning, police said. Others were wounded in a night of violence that had veteran detectives shaking their heads.
Saturday's three killings brought the 2011 homicide toll to 320, the most in three years.
The holiday killing began around 4 p.m. Saturday, when Kevin Moore, 26, was shot six to nine times in Hunting Park while sitting in the front seat of his silver Jaguar. Police had made no arrests as of Sunday night.
Just before midnight, police spotted a green Hyundai idling with its lights on in the 5600 block of North Second Street in the Olney section. Arlette Aguero, 31, of the 4700 block of Tampa Street, and Alejandro Garro, 34, of the 7300 block of Dungan Road, were found shot to death in the front seat.
At 1:30 a.m., Gerard Market, 48, was found fatally shot on the 4100 block of Orchard Street, where he lived.
Around 3 a.m., a 23-year-old man whose identity had not been released Sunday night was found shot in a shoulder at Eighth and Callowhill Streets. The bullet traveled downward, and he died within the hour.
And police ping-ponged across the city throughout the night, responding to nonfatal shootings.
On the 5200 block of Sansom Street, a man opened fire on a New Year's Eve house party, angry over the $5 cover charge. He wounded three people in their arms and legs.
In Testa's killing, Mancuso, of the 1000 block of Ritner Street, was arrested Sunday morning on Jessup Street and charged with murder.
