A few observations about chapters 8 and 9. Coming from someone in/around your target audience who's reading the HTML draft.

I don't get a lot out of chapter 8. The title is enticing, but I was surprised by its brevity. Then chapter 9, also an enticing title, went straight to testing. Diverged from the title. I began to wonder: did I miss something? Who's the target audience again?

Based on that experience, I got the idea that directories, paths, exceptions and warnings from chapter 9 might be something to incorporate into chapter 8. Then 8 would be fleshed out a bit, and could be more about "understanding how perl works", effective perl. Consideration of style and maintainability included. Simplicity, duplication, naming could then be substantiated with code examples (perchance with existing code examples). Continuing that thought, chapter 9 would still discuss testing, modules, cpan, pragmas, importing etc. It could be more about "how to manage perl code", idiomatic perl. Community wisdom/norms, testable code, and modularize, formerly discussed in 8, could then be substantiated with existing code examples.

On the other hand, it's conceivable that both chapters 8 and 9 could get combined into one chapter. As it stands, chapter 8 seems to be missing something. It's like a prelude to 9. But 9 goes straight into the weeds without a second thought. Combining them appears to be a matter of strategically interjecting points from 8 into 9.

Or, on the gripping hand, simply leave these chapters as they are. Although the title for chapter 9 leads me to expect one thing, as I stated, but immediately talks about testing. Including a transitional final sentence in the second paragraph of chapter 9 might be good (e.g. "Testing is one of those many techniques.").

Again, observations.