Williams are not releasing information about Robert Kubica's test that took place at Silverstone this week.
All a spokesman for the British team would say about the Pole's run in a 2014 car was that it had been "successful".
"We will not be releasing any further information at this time," the spokesman said.
It is believed that Williams will follow up Kubica's Silverstone run on Wednesday with a more comprehensive two-day test in Hungary next week.
That test will also be attended by Paul di Resta, another contender to replace Felipe Massa next year.
"We will test those two drivers," team technical director Paddy Lowe confirmed.
"We won't give away any information around what we do within those tests - that's a private matter for us and I would stress that it doesn't mean they're the only drivers under consideration."
The season continues with the United States Grand Prix next weekend.
