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 conveys this by using paradoxical statements and exaggerating the absurd qualities of 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. Characters can be joking about apples one moment, while people are dying the next.