Ferrari's Jules Bianchi led the way on the opening day of Formula 1's young driver test at Magny-Cours on Tuesday.
The Frenchman ended the day half a second quicker than Force India's Luiz Razia.
Bianchi, who has been Force India's reserve driver this year, completed 87 laps, with a best of 1m18.070s, as Ferrari evaluated a new front wing as part of its aerodynamic development programme.
His running came to an early end after he stopped at Chateau d'Eau with an electrical problem.
GP2 title contender Razia, having his first taste of Force India machinery, used soft tyres to set a best lap of 1m18.535s during his 64 laps of running.
His team was trialling a new front wing, and the Brazilian brought out the red flags at one point during the afternoon when he spun at Imola.
Third fastest Sam Bird was the centre of attention during the morning as Mercedes unveiled a new Coanda-effect exhaust layout as part of an update push it is having with its W03. He set a best time of 1m19.094s and completed 95 laps.
Bianchi will switch to the Force India car on Wednesday, as the team evaluates his potential for a race seat next year.
Davide Rigon will take over the Ferrari, while Bird continues evaluation of more Mercedes updates.
Pos Driver Team Time 1. Jules Bianchi Ferrari 1m18.070s 2. Luiz Razia Force India-Mercedes 1m18.535s + 0.465s 3. Sam Bird Mercedes 1m19.094s + 1.024s
* All timing unofficial