Williams rear wing F1 testing focused on 2016 weaknesses

Development driver Alex Lynn gave the double-decker device its first run out on Tuesday, running it for half a day.

Massa took over on Wednesday, running it all day as Williams bids to find more downforce and improve the FW38's balance.

When asked by Autosport how much Williams was able to learn for 2016 and next year, when radical new bodywork regulations come into play, Massa said: "We were able to learn a lot.

"It is the first time we are doing these tests in the proper way, two days concentrating on things which we believe we need to work on the car, knowing where we are losing compared to other cars.

"It's a long project, it's not really things that tomorrow will be completely different specs in the car.

"I believe we are understanding things to make the car better."

Lynn admitted on Tuesday that he did not push the car and Massa said he, too, was not searching for lap times.

"As you can see, we're not here to do lap times, we're here to do future developing of the car," said the Brazilian, who ended the session ninth.

"I hope it's not too much in the future, I hope we can have things that we did here quickly.

"I hope we understood things that can be important to make our car quicker.

"This wing is not making the car quicker, it's making some balance, some different things we are developing to make the car better.

"We are doing tests which we don't need to [give] any details because they are so complicated.

"It was pretty interesting what we did. It was an important test."