The opening in-season test came to an end today, Mercedes once again setting the pace.

Ominously, not only was Valtteri Bottas quickest, beating teammate Lewis Hamilton's best from yesterday, the Silver Arrow completed 143 (almost) trouble-free laps, the most of all present today.

We say 'almost' trouble-free because the Finn caused the day's only red flag when he stopped on track four hours into the session, the issue later traced to the steering wheel.

Though he set the early pace, Sebastian Vettel, who was running until 9pm last night as he conducted tyre testing for Pirelli, lost a lot of track time in the morning as the SF70H encountered a hydraulics issue which necessitated the removal of the back end of the car.

Similarly, at Red Bull, Pierre Gasly, after a trouble free morning the Frenchman was sidelined for much of the afternoon, only competing another 14 laps.

Having shed his T-wing over the course of the last two GP weekends, leading to the FIA having words with his team, this morning Bottas deliberately ran without the controversial device which the sport is seeking to ban for next year.

Though his best time of the day was set in the afternoon with the device attached, he posted an impressive 31.771 in the morning without it.

Having completed 56 laps in the morning, Honda was anticipating the afternoon session, revealing that Vandoorne would be testing new parts. However, as he only completed a further 25 laps in the afternoon we are unsure of their effectiveness.

However, if nothing else, there were no repeats of the MGU-H issue that plagued McLaren's Bahrain GP weekend.

Between them the 12 drivers on duty today completed 1007 laps, which compares with the 844 yesterday when there were also 12 drivers on duty.

For Mercedes, today's programme focused on tyre and aerodynamic analysis, engine development evaluation and setup work to address issues with poor rear grip in Sunday's race.

"Today was very good," said Bottas. "We got so much running done. We were focusing all-day on the long-run pace, which was a bit of a problem for us on Sunday compared to Ferrari.

"We did some interesting tests to try and improve both the tyre life and the race pace," he continued. "We have definitely got plenty to analyse tonight. I think I learned a few tricks today as well.

"To stay here in Bahrain for a test after two back to back races is tough, but the guys have done a great job over these two days of testing. Now we head home for a few days before the next race in Russia."

Today there was no need to extend the test session, consequently at 18:00 local time, Vettel parked the SF70H at the end of the day's work.

The German completed 64 laps on his way to posting the second best time of the day on the soft compound.

Yesterday, Sunday's race winner was on duty for Pirelli, while today it was a normal programme of development for the season.

"It would be nice to have done even more," said the German. "But today we had a few little problems in the morning, which is normal for testing and then, in the afternoon, we lost some time when there was an electrical black-out in our garage."

"The times don't mean much, given we don't know what programmes the others are running," he admitted.

Having run GP2 contender Sean Gelael yesterday, today, Toro Rosso, which had a difficult Bahrain Grand Prix weekend, had its two regular drivers on duty.

Carlos Sainz, who picked up a 3-place grid penalty for Sochi as a result of his clash with Lance Stroll, ended the day third quickest.

"I think we can be very happy with how this test went," said the Spaniard, "both yesterday with Sean and today with Daniil and myself - to have two clean days and be able to test many parts was just what we needed.

"I'd like to thank the team and Renault, as it's been very useful. Overall, I end a positive day with very good feelings and lots of things learned. I now look forward to the next race weekend in Russia!"

"A very productive test for both myself and the team," added Kvyat, "considering it was only half a day, we managed to do plenty of laps, so we can be happy. It's all been very positive and the car is reliable.

"After a very long three weeks, I have to say thank you to all the mechanics for their great effort today - they are tired and still did an impeccable job.

"It was useful to be able to try a few things that are sometimes a bit risky to try in Free Practice sessions during a race weekend, so this was the time to do this. We now have a lot of data to go through and we will use this in order to get ready for my home race in Russia and the rest of the upcoming races."

"Following a productive day yesterday with Sean, Daniil and Carlos took over driving duties today," said Jody Egginton, the Faenza outfit's Head of Vehicle Performance. "The plan was to continue to evaluate the range of new mechanical updates we had available for this test, together with some tyre based tests.

"Daniil's day started well, with some aero dedicated runs, followed by normal baseline setting runs. After this we moved on to some more specific tests, evaluating some mechanical set-up items the results of which were positive. This means we can consider these parts for a race introduction.

"Carlos took over driving duties for the afternoon, running some further aero-dedicated tests and then moving on to evaluate mechanical test items as well as conducting a small tyre test program. All of this happened as planned and some good set-up directions were identified, combined with a good amount of kilometres put on these new parts.

"In summary, as a team, we can be happy with the execution of the test program here in Bahrain. Some positive results have been obtained and this should provide further set-up options for the following races. We now head home for a few days before moving on to Russia for the next Grand Prix, where we will aim to put what we have learned here to good use."

McLaren spent much of the day testing a combination of set-up and handling configurations of the chassis, aero data correlation, and power unit driveability and reliability work. The team concluded a valuable and trouble-free day of running, with Vandoorne completing 81 laps.

"Today has probably been our best day this season so far," beamed the Belgian. "It's the first time that we've had a day without any big problems, where we could actually get on with our programme. I think we completed everything we wanted to do today, and we went through a lot of set-up stuff that we didn't manage to do in Barcelona.

"It's been a very productive day and I'm very happy that we've been able to do so many laps. Especially after a difficult day yesterday and a difficult weekend, it wasn't looking great, but I'm very pleased. For the team, it's not been an easy week, after a double-header and then coming to the test with so many issues. They've been working flat-out, and they've done a very good job to get the car back out on track every time.

"Today was really good, but we need every day to be this good, and there are no guarantees that it will be like this next time. We need to learn very carefully from what we've done today, and hopefully carry that forward to the next event and see some improvements. It's been very good for both me and the team to be able to try a number of different directions with the set-up. There were some new bits on the car - quite fundamental things - that we wanted to try out, and learn about, so it's been really useful to see where the performance comes from, and very productive.

"Today and all weekend I've actually felt very comfortable in the car. The chassis is behaving well, and we'll bring some more new bits to the car over the next few races. The key is to be able to have a weekend where everything runs smoothly, which we haven't been able to do yet. If we can do that, hopefully we can show we are making progress. We just need to keep working hard and wait for the moment when everything falls together."

"Everything has worked perfectly today in terms of reliability, and we were even able to push a little bit in terms of settings," added Eric Boullier. "We've managed a 'proper' test today, and really made the most of every opportunity out on track. Everything we've planned, we've tested, and we've done back-to-back runs, so I'm really happy with the work we've completed today.

"It's complicated to understand the issues we've had over the past few days," he admitted, since today we've managed to run without any problems, but Honda are working hard to understand where the weaknesses lie. We've been able to run with a more aggressive set-up today, gathered a lot of information and tested a lot of solutions, so in terms of both data and results it's, been a very positive day of testing.

"It's certainly been a trying couple of weeks for everyone at McLaren-Honda, and I can't thank the team enough for the long hours, hard work and incredible effort they've put in after a long period away from home. Oliver and Stoffel, too, have both done a sterling job, and, for Stoffel in particular, the mileage we've been able to cover today after difficult back-to-back race weekends for him has been priceless.

"Being able to do a good amount of running on the final day has come at the right time. Now, we'll head back to the factory with even more motivation to keep pushing forward. It's a quick turnaround to crunch the numbers and prepare ourselves for Sochi, which for sure will be another tough weekend for us, but, as always, we're ready for the challenge."

"Despite having a disappointing first day of testing yesterday, today we were able to conduct our plan in accordance with the original schedule and completed 81 laps of useful running," said Satoshi Nakamura. "After facing MGU-H issues during the Bahrain Grand Prix, we made concerted efforts to analyse the issue in a short period of time ahead of this test.

"Based on this analysis, we implemented provisional countermeasures against the issue on our PU and we think we were able to confirm the direction of our solution with today's running. We also made some progress today with the set-up of our PU in order to acquire better driveability and reduce the vibration.

"I want to thank all the members of the McLaren-Honda team who worked tirelessly throughout the days and nights to prepare for the test, even after the tough grand prix we had here in Bahrain.

"Although we are still in behind our competitors in terms of performance, we are confident that we're heading in the right direction. We believe our PU still has more potential and we will continue our development utilising all of the information we have gathered from this test in order to close the gap to our competitors as soon as possible.

"We have less than 10 days to go before the Russian Grand Prix, and we are expecting another tough race there. However, we will keep fighting hard together with McLaren in order to move forward."

Check out our Wednesday gallery from Bahrain, here.