Nikita Mazepin will complete 12 days of testing with Mercedes this year in a W08 car.
Mazepin, a GP3 race winner and 2018 runner-up, will complete 12 days of testing for the Silver Arrows this season in their W08.
However, the agreement between the two parties does not mean Mazepin will be contracted to Mercedes - who already have two reserve drivers, former Force India man Esteban Ocon and now Williams driver George Russell.
Ocon will be able to assist the 19-year-old in a coaching role.
Mazepin already has some testing experience in Formula 1, due to his time as a development driver at Racing Point (formerly Force India).
Over the last three years, the GP3 driver has completed just eight days of testing for Force India.
Mazepin made his debut for Force India back in 2016, with the Russian driver impressing at Silverstone for the team in testing.