Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
That Catch-22 is a parody is quite clear. Heller expresses it by using many paradoxical statements and exaggerating the absurd qualities of all his characters. Although the tone is at times light-hearted and tongue-in-cheek, at other times, it becomes very serious. This fits the themes of the work, and seems to comment on the absurdity of war. While characters can be joking about apples one moment, people are dying the next.