Formula One rivals Nick Heidfeld and Antonio Pizzonia will test head-to-head in Spain on Friday in a session that could decide who races for Williams next year.
A Williams spokesman, however, rejected a suggestion that the Jerez test, the last before the New Year, had turned into a 'shoot-out' between the German and Brazilian hopefuls.
"We are continuing our process of evaluating Nick and seeing how he stacks up against Antonio," he said. "The two will be on the track at the same time but we know already pretty much what Antonio is capable of.
"We have also got components to test and we still have a work load to deal with. It's not just about driver evaluation."
Pizzonia has been the team's test driver all year, filling in for the injured Ralf Schumacher in four races, while Heidfeld has more experience of Formula One but only drove the Williams for the first time last week.
Pizzonia was the pre-test favourite but Heidfeld, 27, has made a big impression, and the quiet man from Moenchengladbach can also count on strong backing from engine partner BMW.
He made Williams take notice with his performance in wet conditions and the team asked him to return this week before making any decision about who partners Australian Mark Webber next season.
"In the rain, Nick is truly fast," race engineer Tony Ross said on the Williams website. "And he knows exactly what he wants when working with the car. Unfortunately, the track was never completely dry. Now, during his second test for us, we want to find out how he will perform in dry conditions."
Heidfeld tested with Webber on Thursday, completing 126 laps on his way to a time of 1:17.558 minutes. Webber lapped in 1:17.514 but his running was limited to 76 laps after requiring an engine change.
McLaren's Kimi Raikkonen was fastest in 1:16.658.