Sebastian Vettel heads the timesheets in the morning session of day two in Bahrain.
The German took over duties from Mick Schumacher, who is driving the Alfa Romeo today after testing the Ferrari on Tuesday.
After the first four hours, Schumacher is down in ninth place, having had little running in the opening two hours.
After crashing the Racing Point car late on yesterday evening, Stroll was second for the Silverstone squad, and he will now hand the car over to Sergio Perez, who scored a point in Bahrain last Sunday.
George Russell is third, as he tests the Mercedes W10. He leads Alexander Albon and Pietro Fittipaldi, who drove the car for one hour yesterday following the end of the rain delay.
Lando Norris was sixth, ahead of Dan TIcktum, who makes his F1 test debut with Red Bull Racing. Carlos Sainz tested for Pirelli, and finished his duties as Fernando Alonso takes over the McLaren seat.
Daniil Kvyat is also testing for Pirelli and is currently two spots behind Sainz. Jack Aitken is just outside the top ten, while Nicholas Latifi, who was scheduled to test in Barcelona but missed out due to the late arrival of the FW42, was last of the morning runners.