The four-time World Cup champions crashed out at the group stages in Brazil, finishing third behind Costa Rica and Uruguay after two defeats in three games.
Cesare Prandelli stepped down from his role as coach, leading to Antonio Conte's appointment and the former Juventus boss' reign started with a win after Italy defeated the Netherlands 2-0 in an international friendly on Thursday.
Italy are now preparing to face Norway in their opening Euro 2016 Group H qualifier on Tuesday and Buffon said the Netherlands result bodes well for the trip to Oslo.
"The other day we faced a team that played a friendly match, that seems clear to me," the 36-year-old said.
"A team like Holland that goes down two goals and is playing without a man after eight minutes is odd, but we played a big part in that result, too.
"In the last few years, the best way to test our focus was to see how we fared in the friendlies, where it has happened time and time again to play very badly and raise alarms. I think this was a very convincing response from us.
"In a game that for a thousand reasons could have been very tricky for us, especially because it was a friendly match, after eight minutes we were ahead 2-0.
"Our mental approach to the game was spot-on this time."
