The Obama campaign must have stayed up late trying to come up for some explanation for Biden's "world testing" commentary. The best they could do is this, as reported by CBS News:
“You know I think that Joe sometimes engages in rhetorical flourishes,” Obama said. “But I think that his core point was that the next administration is going to be tested regardless of who it is.”
Meanwhile, Biden decided to practice being Dick Cheney by moving to an undisclosed location away from the press -- just in case there is world testing between now and the election, of course.