Most code is buggy. Even the very best code can still have bugs, which means the ability to find and eliminate bugs is a critical skill for all software engineers. If you don't know how to find the bugs your users find, you're in trouble. Which is why we cover bug hunting in the chapter entitled
Chapter 6, Debugging_the_Code, and we cover the mechanics of fixing code in the chapter entitled
Chapter 7, Fixing_the_Code.