Williams kick-started the Formula One group test at Jerez on Monday as Dani Clos hit the track in Spain.
The Formula 3 Euroseries racer was the only person on track during the first day of testing, with other teams due to start their programmes today.
With the Spaniard tasked with set-up and slick development work, wet conditions during the morning weren't ideal but the circuit began to dry out by early afternoon allowing Clos to complete nearly 80 laps on his single day on track.
“Today we ran Dani Clos in the FW30B interim car and concentrated on development work of the KERS and general chassis set-up work,” test team manager Dickie Stanford said. “Tonight we will convert the car for Kazuki who will take over driving duties tomorrow [Tuesday].”