Fernando Alonso said he felt "good potential" in Renault's Formula One car during his test at Barcelona's Circuit de Catalunya on Tuesday.
The 100km test is part of Alonso's preparation for his return next year, when he will take the place of Daniel Ricciardo. The two-time world champion left F1 at the end of 2018 after four disappointing seasons with McLaren.
"I think the car was a nice surprise," Alonso said on Tuesday. "We know the car is performing well at the last couple of races and I felt the grip and certainly good potential in it.
"The last time I drove a Renault engine was in 2018 and I felt a step forwards, which is quite important there. Everything felt good.
"I wasn't able to maximise the performance of the car because I'm not up to speed yet, but I'm happy with the day."
Alonso's test came just two days after Ricciardo took Renault back to the podium at the Eifel Grand Prix, its first top-three finish since returning to the grid as a manufacturer team in 2016.
Asked if that result made him even hungrier for success, Alonso replied: "I'm still the same after Sunday. I know what the team is capable of and I know the prospects for the future are good. The podium is a thing that had to happen. Most important thing is to follow the trend that we see now, keep the momentum into next year, especially for 2022, and I think we know how to do it."