Barcelona: Nico Rosberg of Mercedes was the fastest on the last day of Formula One's final test on Saturday under heavy rain at the Catalunya Circuit.
With poor weather conditions limiting action for most of the day, Rosberg came on late to set the best time of 1 minute, 43.814 seconds.
"It was tricky out there today. There wasn't a lot of grip, but it was really useful to get the experience on the Pirelli wet tires," Rosberg said. "We have made a lot of progress over the four tests this winter and it's really nice to see that things are going in the right direction."
Pastor Maldonado of Williams was 0.519 seconds behind, and Lewis Hamilton of McLaren was the third fastest at 1 minute, 44.560 seconds.
Rosberg's teammate Michael Schumacher and Fernando Alonso of Ferrari were the only other drivers to venture out on the wet track but neither posted times.
"We tested a couple of things during some shorter runs, but it was very dangerous out there," Hamilton said. "The championship is open, and we don't know what to expect."
Mercedes heads into the season's first race on March 27 in Melbourne boosted by a new aerodynamics package. On Friday, Schumacher clocked the best time of the Barcelona test at 1 minute, 21.249 seconds, while Rosberg finished third.
"We've had a very productive test in Barcelona working on the final specification of the (new car) for the first race of the season in Australia," said Mercedes team principal Ross Brawn. "Both drivers and the team have achieved a good amount of work for the new season in terms of race weekend simulations and it is now down to the final preparations for the first race."
The last time a Brawn-led team led the final session of preseason testing - with Brawn GP in 2009 - it went on to win the championship, with current McLaren driver Jenson Button as the world champion.
Hispania were unable to race on Saturday after car parts were held up in customs.
The Australian Grand Prix will open the season after the Bahrain GP was canceled due to political unrest in the region.