Valtteri Bottas says the Jerez test was positive for Williams, despite using a development version of their 2012 car and not posting very competitive times.
Williams was the only team not to debut their 2013 car, the FW35, in this week's opening test in Spain, opting instead to prioritise more development time in the wind tunnel.
Last year's FW34 was modified to include a number of 2013-spec developments - particularly a Coanda exhaust - but Bottas and team-mate Pastor Madonado still did not manage to finish higher than eighth on the timesheets, finding themselves a good two seconds off the pace on each day.
Williams did rack up 92 laps on Friday's final day of testing, however, clocking a best time of 1:19.851, and Bottas said the experience was far from a waste of time.
"We've got some positive results and the whole test basically was really positve for us," said the rookie.
"We got a big amount of data to analyse so the guys will be working really hard now to find which are the best bits to put [forward] for the new car."
Asked why Williams failed to set a truly competitive time in a car that they were far more familiar with, Bottas replied: "There's a simple reason: the physics still exist - if you have lighter car with less fuel it goes a bit quicker!"
The Finn added that they were able to test a number of new parts in the old car, getting a good idea of which ones to take forward onto the FW35.
"Barcelona test one will be really important for us, new car, so a lot to go through. But this test has still been really valuable to understand the tyres," he told Sky Sports F1.
"The conditions were maybe not ideal for tyre testing but it's the same for everyone. We managed to test a lot of new parts in the old car here and we got some really good data. We have quite got quite a good understanding now which direction to push for and which parts to put in the new car."