Renault was forced to sit out the bulk of the afternoon session at the Circuit de Barcelona-Catalunya after Jolyon Palmer's RS16 suffered a power unit component failure.
Palmer brought the red flags out half an hour into afternoon running on the approach to Turn 3, with a small amount of smoke trailing from his car.
Palmer ultimtely ended the day in 10th place, having completed 42 laps, the fewest of any of the drivers.
"The positives from today are immediately apparent," said an upbeat Palmer.
"We were able to run a good programme in the morning, covering a lot of what we wanted to do.
"The car feels good and forgiving and provides a great baseline for us to work forwards.
"Unfortunately we did stop running early in the afternoon, but my overall analysis of today is most certainly positive."
Formula 1 returnee Kevin Magnussen will make his Renault testing bow on Wednesday.