Kimi Raikkonen completed a successful first pre-season test for Ferrari by setting the pace on the final day at Spain's Jerez track.It is the third time in four days a Ferrari has been fastest, as the teams reached one-third distance in their preparations for the 2015 season.
Sauber's Marcus Ericsson was second ahead of Lewis Hamilton, whose Mercedes team completed by far the most mileage.
McLaren had another tough day, still struggling with their new Honda engine.
Jenson Button did only 35 laps and was 6.8 seconds off the pace as he was hit initially by a problem with oil levels and then was forced to abandon the day's running following a fuel-pump failure.
McLaren posted 79 laps over four days - compared to more than 500 by Mercedes. But director of engineering Matt Morris insisted the team had had a positive test as they bedded in their relationship with Honda.
"We have had a number of problems," Morris said. "We have had some operational issues - all of us working together as a team for the first time - things you take for granted when you have been with an engine supplier for many years.
"We have also had some minor electrical issues, which resulted in a lot of downtime but have actually been relatively easy to fix.
"The main thing is that we have not been burning bodywork or blowing up engines.
"I am pretty happy that we are going to come out of this test with no major issues to resolve."
Hamilton had a harmless spin at the chicane in the morning but still managed 117 laps as Mercedes completed an impressive overall distance of 1,419 miles in four days.
Hamilton told his team over the car radio: "Well done, guys. Great first week back."
On his spin he said: "It was a bit damp, I was the first on slicks, so I just had a spin.
"But reliability has been pretty special this week. It's one of our highest weeks of mileage.
"The car feels very similar to last year. It's very difficult to pick out any differences, really."
Lotus also had an encouraging final day as they completed their first test with a Mercedes engine, after switching from Renault last year.
Frenchman Romain Grosjean was sixth fastest and his day was ended by an engine problem, but the team said they were confident the car was a major advance on last year.
"It's a shame it's ended early," said trackside operations director Alan Permane. 'It's been going really well, especially as a week ago we did not even expect to be here.
"The car is most definitely a big step forward over last year, even though we are still short of a lot of parts so it's not very representative.
"It's surprising we were running as quickly as we were given that. It's very encouraging - in fact, Romain was just saying that the car feels a lot like the 2013 car. He's a lot happier.'"
The second test is at Barcelona's Circuit de Catalunya from 19-22 February.
Fastest lap times, final day of first pre-season test in Jerez1 Kimi Raikkonen (Fin) Ferrari 1:20.841
2 Marcus Ericsson (Swe) Sauber-Ferrari 1:22.019
3 Lewis Hamilton (GB) Mercedes 1:22.172
4 Max Verstappen (Ned) Toro Rosso-Renault 1:22.553
5 Felipe Massa (Brz) Williams-Mercedes 1:23.116
6 Romain Grosjean (Fra) Lotus-Mercedes 1:23.802
7 Daniil Kvyat (Rus) Red Bull-Renault 1:23.975
8 Jenson Button (GB) McLaren-Honda 1:27.660