Gasly had been a contender for a 2015 race seat with the team, but ultimately lost out to Carlos Sainz - whom he also finished runner-up to in Formula Renault 3.5 last year.
The 19-year-old Frenchman's outstanding record in junior formulae also includes winning the Formula Renault 2.0 Euro crown in 2013, a title previously won by McLaren protegee Stoffel Vandoorne. The pair will both compete in GP2 this year.
The Barcelona test, one of two in-season tests in 2015, takes place on May 12-13 - immediately after the Formula 1 Gran Premio De Espana Pirelli 2015. Austria's Red Bull Ring hosts the second test on June 23-24.