When Athena appears to Odysseus in her disguise, Odysseus becomes an actor himself. He pretends to be a poor wanderer who was abandoned by his hosts. This is ironically true, but nonetheless, he acts like he isn't Odysseus. She knows it is him and the two have a laugh.
This shows that Odysseus still has a sense of humor after all that has happened to him. It also shows that their relationship is solid. When friends who haven't seen each other for some time can verify identity through sneaky means it demonstrates great understanding of each other. This test also demonstrates and foreshadows Odysseus' ability to do what he needs to do in the upcoming books.