It will be the first time that the two famous drivers have gone head-to-head in the same car at the same circuit, and the occasion is therefore certain to draw much attention in the racing world.
Schumacher, 39, is scheduled to hand over the F2008 to Raikkonen's current teammate Felipe Massa for the other two days of the test at Montmelo, a municipality north of Barcelona in Catalonia, Spain.
In recent months, the German has previously tested for Ferrari at Barcelona and Jerez.
Meanwhile, at the Circuit de Catalunya on Friday (today), Ferrari is exclusively conducting a full race simulation, with Massa and official test driver Luca Badoer in command of the cars.