The British team will run the Norwegian alongside its 2012 driver Jolyon Palmer and Facu Regalia at the Spanish circuit on October 30-31.
Varhaug failed to score a point during a full-time GP2 campaign in 2011 with DAMS, but won three times on his way to second overall in Auto GP this year.
Palmer, meanwhile, won at Monaco in GP2 this season and finished 11th in the championship. Argentinian driver Regalia was seventh in Auto GP and also dabbled in GP3 and the European F3 Open.
Team principal Paul Jackson said: "It is always interesting when you have new drivers in the team, to see how they work with the engineers and how you can help them develop, so this test will let us see how these two young drivers shape up against Jolyon.
"Pal has previous GP2 experience, so we expect him to be comfortable quite early, while Facu will be new to GP2 and will take a little more time to get settled.
"We look forward to a productive test."
Regalia will also drive for rival squad Racing Engineering at Barcelona, alongside GP2 racer Nigel Melker, Formula Renault 3.5 graduate Andre Negrao and F3 Open title favourite Gianmarco Raimondo.
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- Motor Racing
- Jolyon Palmer
- Facu Regalia