The end-of-season test came a day after Toyota won the Six Hours of Bahrain race at the track.
"It was a great day. Testing an LMP1 (Le Mans top tier) car is always a nice thing for any racing driver because these cars are amazing to drive," Alonso said in a Toyota statement.
"They are very consistent throughout a stint which is a positive thing. I have wanted to test a car like this for a long time now and today I could achieve that so I am happy," added the Spaniard.
Alonso, who will be racing in Formula One's Abu Dhabi season-ender next weekend, posted a best time of one minute 43.013 which compared to a 1:42.38 set by Toyota regular Mike Conway.
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The Spaniard had visited Toyota's Cologne factory in Germany on Nov. 7 for a seat fitting and simulator session.
McLaren are partnered by Honda, Toyota's big domestic auto industry rivals, but that relationship will terminate at the end of this season -- leaving Alonso free to race for Toyota at Le Mans without contractual problems should he secure a drive.
Le Mans in June does not clash with any Formula One commitments.
Toyota have yet to confirm their continuation in the endurance championship, with champions Porsche pulling out, but are expected to stay as favourites to win Le Mans.
Alonso, who competed in this year's Indianapolis 500, has set his sights on completing the so-called Triple Crown of motorsport.
The feat, only achieved by the late British driver Graham Hill, involves winning Indianapolis, The Le Mans 24 Hours sportscar car and the Formula One world championship.
Some consider the Triple Crown to be the Monaco Grand Prix, rather than the world championship, but Alonso has won both.
He will also compete in the Daytona 24 Hours race in Florida in January with the United Autosports team as part of his preparations.
(Reporting by Alan Baldwin in London, editing by Toby Davis)
