Renault have hailed as a success the first test of their new Grand Prix car.
Trulli said he was pleased by the feel of the new car
Jarno Trulli, who was the first man to drive it in at Barcelona, said: "The car was well-balanced and responded well to the changes we tried."
Renault's executive director of engineering, Pat Symonds, described the results of the test at Barcelona on Tuesday and Wednesday as "very good".
Trulli was 10th fastest in the test, 2.1secs slower than pace-setter Ralf Schumacher in the 2004 Williams.
Technical director Bob Bell added that the test had marked a "very promising start".
The car has a similar look to its predecessor, which won the Hungarian Grand Prix in the hands of Fernando Alonso, but has more sculpted and lower sidepods.
It also features a brand new engine after Renault decided to ditch their radical wide vee-angle V10 in favour of a more conventional unit this season.
Trulli ran into reliability problems on Wednesday, but still managed to complete nearly 200 miles worth of running, the team said.
Button was quick in the development BAR-Honda
Alonso is scheduled to take over the car on Thursday.
Williams dominated the times on both Tuesday and Wednesday, with Juan Pablo Montoya second fastest behind Schumacher on both days.
Alonso was third fastest on Tuesday and Wednesday, ahead of Rubens Barrichello in a development version of the 2003 Ferrari.
Jenson Button set the fifth fastest time in the BAR-Honda test car on Wednesday.
Sauber, Toyota, Jaguar and Jordan are also at the test and Williams are giving another chance to young hopeful Nico Rosberg, son of 1982 world champion Keke Rosberg.