As he walked further and further into the forest, he realized that there weren't any rockworms. He looked behind every tree, every blade of grass, and every mound of dirt he saw but there wasn't any sign of rockworms. He decided to exit the forest and ask someone where they were.
He went back into town and started asking people. No one was able to tell him where they were, so he went back to the school to ask the person who gave him the test. He saw the man outside the door waiting for him to come back. He walked up and asked where the rockworms were. The man just laughed and walked inside, waving for him to follow.
As they walked into the school he asked again why he couldn't find any rockworms. The man said that it would be impossible for anyone, no matter who it was or how powerful they were, to find even a single rockworm because they had all gone extinct over a thousand years ago. He asked why he was given the test if it were impossible. The man told him it was just a trick he always plays on the new people that want to become slayers, just to see how much research they actually did about becoming a slayer. Knowing that most people know nothing of being a slayer makes it easy to trick them into wasting their time. To actually get into learning how to be a slayer, he has to do research on everything about them.
He headed to the library in the school to do hours, maybe even days of research, on becoming a slayer. Even though it was only temporary, he was willing to spend years on becoming a slayer. He started the research and realized instantly that this was going to be a difficult job to have.