How do i know if a friend is really my friend?

In school I had 2 friends that were really nice and I liked hanging out with. Now that summer has started, I haven't heard from either of them at all, they said that they would lemme know if they wanted to hang out and stuff. I haven't gotten any texts or calls, or even messages on facebook from them. However, I see them writing on each others facebook asking if they want to hang out. Are these guys really my friends?