What investigators found was that the homemade fertilizer bomb would have created a large explosion with deadly consequences, killing untold numbers of people in the heart of New York City.
But in conducting its test that involved recreating an urban street scene in rural Pennsylvania, the agency failed to notify any state authorities.
Several officials in Centre County, where State College is located, said they didn't know about it either, but it remains unclear in which county the blast took place.
Asked by this reporter on Wednesday whether he had heard about the test, Rendell said he had not, nor was he concerned about not having been informed.
"There's probably not a law against blowing up a vehicle on private property, presuming it didn't hurt anyone," said Rendell, after testifying before the Senate Transportation Committee about the need for new transportation funding.
Neither the ATF, nor the Philadelphia office of the FBI knew about it either. Nor did the Pennsylvania State Police or the Pennsylvania Emergency Management Agency, which has a close working relationship with the FBI, officials said.
"We don't know anything about that," said PEMA spokeswoman Ruth Miller, responding to a request for information.
Several Centre County officials said they too were unaware of the June test, but added that FBI and ATF investigators have used the area's vast gravel and asphalt quarries for similar explosives tests in the past.
In the most recent high-profile, if hush-hush, test, FBI officials told the Associated Press that investigators used a Pathfinder, the same vehicle that was found emitting smoke on a side street off Times Square on May 1, but rigged it with a higher grade fertilizer and more sophisticated components.
Four other vehicles were positioned around the car bomb in positions replicating cars in an adjacent traffic lane and parking spots in Times Square.
The explosion obliterated the SUV, cutting it in half, the officials said. It also turned the car next to the SUV into a flaming wreck, and sent it flying for a distance that in Times Square would have vaulted it over a car parked across the street and into the New York Marriott Marquis.
Two other cars were left in one fiery, tangled wreck in the middle of the mock street, the officials said.
The video was played for a group of law enforcement officials this week.
Dan Surra, a former legislator, now the governor's senior adviser on the Pennsylvania Wilds tourism region, said he was surprised the FBI didn't tell anyone in the state government.
"You shocked the hell out of me," said Surra, who represented Clearfield County, which abuts Centre County and could have been the site of the tests. "It's more disturbing that they didn't tell anyone then the fact they did it."
A spokesman for state Rep. Scott Conklin (D., Centre), the Democratic nominee for lieutenant governor, who traditionally chairs the Pennsylvania Emergency Management Council, said he didn't take issue with the FBI's secret test.
"Our office was unaware of it, but I don't think we would have been informed," said Tor Michaels, Conklin's chief of staff. "There are remote places so such a test could take place without harm to the public. And if it helps learn more about preventing terrorism and keeping us safe that's a good thing."
Faisal Shahzad, a Pakistani-American, is being held in federal custody in New York after pleading guilty last month to all charges related to the terrorist plot.
He told authorities the bomb was supposed to explode within five minutes as he walked away. But instead the explosives only released a stream of smoke that attracted the attention of a street vendor, who notified police.
Federal agents arrested Shahzad two days later as he attempted to flee the country on a Dubai-bound jetliner.
Contact staff writer Amy Worden at 717-783-2584 or firstname.lastname@example.org.
Staff writers John Shiffman and Kathleen Brady Shea contributed to this article.