Spaniard Alonso, who until now has been regarded as Ferrari's clear 'number 1' driver, will make his debut in the 2014 car later in the same test, completing the four-day session.
Raikkonen, arriving from Lotus, has recently been recovering from back surgery that meant he missed the final two races of the 2013 season.
"He is returning to us because we have new technical regulations next year and we need an experienced driver next to Alonso," Ferrari president Luca di Montezemolo is quoted by Germany's Welt newspaper.
"I am convinced that Kimi Raikkonen will meet our requirements better than Felipe Massa.
"Some people are calling it a big risk," he added, "but I have been here since the early 70s and I know that risk is something you have to live with in formula one."
Montezemolo is referring to suggestions that, while Alonso and Massa was a harmonious pairing, adding 2007 world champion Raikkonen to the lineup might only further antagonise the already frustrated Alonso.
Spaniard Alonso, however, has played down claims he is already stamping his feet about having to take on Raikkonen.
"I'm excited to work with him," Brazil's Agencia Estado quotes him as saying, "because he has an extraordinary talent and he is Ferrari's last champion.
"I can learn a lot from him," Alonso added.
He said it is wrong to say Ferrari's new driver lineup will be too explosive.
"I cannot comment," he is quoted by Spain's El Pais, "because I don't know him, I haven't worked on a team with him or shared more than 10 minutes with him."
Some days ago, Alonso suggested Ferrari will "miss" Brazilian Massa's devoted efforts and open personality, which was interpreted by some as an early slight against Raikkonen.
"I'm not at all worried about such things," Montezemolo is quoted by Finland's Turun Sanomat.
"Kimi will be Kimi, the same driver he has always been. If he spoke a lot, he would not be Kimi.
"I can see he is very motivated to be with Ferrari again, after he had to pause for a while after his last period with Ferrari," Montezemolo explained.
"That was very important for him, as he came back very hungry for success."
He insisted Raikkonen will even be happy to work in Ferrari's new driver simulator, despite earlier reports that said the Finn is no fan of the technology.
"We now have a pretty good simulator at our disposal, and I think Raikkonen is happy to work with it," said Montezemolo.
He stopped short of saying Alonso remains the number 1, but he did allude to a hierarchy: "I think Fernando is the strongest racing driver in the world.
"He has a highly motivated new teammate. I look forward to both drivers getting a lot of points, so that we can fight back in the constructors' championship," said Montezemolo.
And he is not expecting fireworks between the pair.
"(Team boss Stefano) Domenicali has been very clear with them," Montezemolo is quoted by France's autohebdo.fr.
"They have the honour and responsibility to drive for Ferrari. If drivers want to drive for themselves, they can make their own team or they can move somewhere else.
"But at Ferrari, there are very clear rules," he insisted.