Pascal Wehrlein had been due to drive for Force India on Tuesday, with Nick Yelloly taking over on Wednesday. However, the team was forced to put Yelloly in the car on the opening day due to Wehrlein suffering from a fever, and with the young German driving for Mercedes on day two he will be unable to run in the VJM08 this week.
Force India has therefore turned to 18-year-old Ocon, who was previously development driver at Lotus. Ocon won last year's FIA European F3 championship - beating Toro Rosso's Max Verstappen to the title - and marked his debut GP3 race weekend with victory in Barcelona.
Ocon is another driver affiliated with Mercedes, with the team announcing it would be providing support to his career last week, and also revealing an option to sign him as a "fully fledged Mercedes-Benz driver in the future".
@OconEsteban will complete our test line-up this week when he drives the VJM08 tomorrow. Great opportunity for a very promising young talent
— Sahara Force India (@ForceIndiaF1) May 12, 2015
For live coverage of the opening day of testing, click here
Click here for Tuesday's gallery from testing at the Circuit de Catalunya