Sakhir runs put mileage on new-for-2015 drag-reduction system in Formula One's feeder series.
Reigning GP3 Series title winner Alex Lynn drove the GP2 development car at Sakhir International Circuit, as part of his prize for winning the crown last year.
The main purpose for the test was aero-testing, to put mileage on the DRS and to work on its reliability for the upcoming season.
The 21-year-old Briton, who is a Williams F1 reserve driver and will drive for champions DAMS in GP2 this year, spent his morning focusing on straightline aero tests to help capture data for all teams in the season ahead.
His afternoon focused on long runs on the 5.412km track, to test and further the reliability of the newly-added DRS.
"I have really enjoyed driving the GP2 development car today," said Lynn.
"It has been a very studious test session so far. I am grateful for this prize and opportunity.
"I would like to thank the Series and I hope that my feedback will be a benefit to all of the GP2 teams regarding the newly-added DRS."
Lynn will continue his test session for a half-day period tomorrow in Bahrain.