The wet weather will be a blow to McLaren's preparations
By Andrew Benson and Sarah Holt
The final day of Formula 1 testing was hit by heavy rain at the Circuit de Catalunya near Barcelona.
It is a blow to McLaren, who have been struggling with an uncompetitive and unreliable car ahead of the first race in Australia on 27 March.
But Lewis Hamilton insisted the team would get back on track, telling Autosport.com: "We know we have a bit of a hill to climb, but we can do it."
McLaren were joined on the final day by Ferrari, Mercedes and Williams.
Conditions improved marginally in the final hour and Mercedes driver Nico Rosberg set the fastest time of the day in one minute 43.814 seconds. Williams's Pastor Maldonado was 0.519secs behind the German and Hamilton 0.746secs adrift.
Rosberg said: "It was tricky out there; there wasn't a lot of grip, but it was really useful to get the experience on the Pirelli wet tyres.
"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.
"We are on the up for sure, and all credit to the team for getting the upgrades on the car and, most importantly, to see that they are working as expected."
Ferrari's Fernando Alonso and Mercedes driver Michael Schumacher did not record a timed lap and Ferrari packed up two hours early, having done five incomplete laps to practice some wet starts.
McLaren are the only team who are yet to do a race simulation with their new car apart from backmarkers Hispania, who only unveiled their new car on Friday and have not run it.
That means there are big question marks over the reliability and pace of the car that Hamilton and team-mate Jenson Button had hoped would take them to a second drivers' title.
Hamilton said: "I don't like to use the word 'frustrating' because I'm not frustrated.
"It's tough on everyone in the team because everyone puts so much work into it, and you see it come out and look so beautiful, and... it's not a disaster, it just doesn't have as much performance as we'd like at the moment. But it's a foundation that we can build on, and that's all that really matters.
"It means that we can get there. If you look at last year, we didn't have the fastest start at the beginning but we were there or thereabouts and second in the constructors' championship.
"It's a long, long year and I have no doubts that we can compete with these guys."
There has been almost no wet-weather running in testing so far this winter but the rain on Saturday was so heavy that the teams were not even able to finally get some serious running on wet tyres.
Pirelli have taken over from Bridgestone as F1's sole tyre supplier this season and there has been almost no running in the wet this winter.
A statement by Ferrari said: "Track conditions are very difficult, as can be seen from the fact that just one driver, Hamilton, has completed any timed laps.
"All the others, including Fernando, made do with some out-in laps, broken up with some practice starts which are always useful."
Hispania had planned to test on Saturday as well but
have been forced to call off their programme
after parts for their new car, which was unveiled on Friday, were held up in customs.
That leaves the team heading to the first race with no testing of the new car.
Schumacher set the fastest lap of the winter at the Circuit de Catalunya on Friday
after adding a raft of upgrades to the car.
But the weather on Saturday means his team will now go to Australia without having done a race-distance run with the car in its new specification.
Insiders say this is not a major concern as they have done race simulations with the car in its previous spec.