Williams' 2013 car will not be present at the first pre-season test as the team will only launch the FW35 at Barcelona on 19 February.
The team announced on Friday that although they will be present at the first pre-season test at Jerez in early February, their new car will not be available.
"For the earlier Jerez test starting on the 5th February, the team will run the 2012 FW34 in order to test a number of key development parts in preparation for the launch of the FW35," said a statement.
The team added that the new car, the Williams Renault FW35, will be unveiled on Tuesday 19 February at the Circuit de Catalunya in Spain.
The car, which will be rolled out of the garage for a photocall with drivers Pastor Maldonado and Valtteri Bottas in the morning, will hit the track later that day for the start of the second pre-season test at the Barcelona circuit.
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