Williams reserve and development driver Robert Kubica believes he's already got a good idea of the relative strengths and weaknesses of the team's new FW41.
Kubica completed 122 laps in the new car during two weeks of pre-season testing at the Circuit de Barcelona-Catalunya. He gave up his half-day behind the wheel on the final day to allow Lance Stroll more time in the car.
"Thursday morning was enough for me to understand the car to the point that I can describe its strengths and weaknesses to the engineers," he said.
"I have a clear idea of where to improve the balance and the feel of the car.
"From my point of view, from the goals we had and in the position I am, I think I had quite a clear view of where we have to do some work," he added.
"There are still issues with the behaviour of the car and the sensitivity of the car to the tyres.
"We have to make the tyre window larger in order to give Lance and Sergey confidence. It's important because they're still quite inexperienced."
But he wouldn't go into any further detail about the car's current faults. "That's something that will stay in the engineers room," he said.
Kubica had originally hoped to be part of the full-time driver line-up at Williams in 2018. However, he lost out to Russian rookie Sergey Sirotkin and was handed a test role at the team instead.
The 33-year-old Pole said his new responsibilities were giving him a welcome fresh insight into Formula 1.
"I am enjoying my position," he told Autosport magazine. "When you are a race driver you don't get so deep.
"When you are a race driver, you see things in the race driver mode," he explained. "The engineers, technicians, mechanics, all the team is working. But when you are a race driver you don't get so deep as I have.
"It's giving me quite a lot of challenges and also opportunities to see the team working, to see different point of view of many things.
"I'm enjoying it. It's also good fun. I think it will be an interesting year."