Force India, who have Germany's Nico Hulkenberg and Mexican Sergio Perez as race drivers, use Mercedes engines.
Juncadella, 22, will take part in several Friday practice sessions and attend all races as well as working on the factory simulator.
"It's a fantastic opportunity for me to learn and will hopefully take me a step closer to eventually racing in Formula One," said the Spaniard, the 2012 European Formula Three champion who tested with Williams last year.
Britain's James Calado was Force India's reserve last year.
Several other drivers, including Hulkenberg and Frenchman Jules Bianchi, have used the role as a stepping stone to a Formula One race seat.
Image: Daniel Juncadella
Photograph: Sahara Force India Formula One Team
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