Claude Code: Up and Running

Chapter 4. When Vibe Coding Isn’t Enough

A Note for Early Release Readers

With Early Release ebooks, you get books in their earliest form—the author’s raw and unedited content as they write—so you can take advantage of these technologies long before the official release of these titles.

This will be the 4th chapter of the final book. The GitHub repo is active.

If you’d like to be actively involved in reviewing and commenting on this draft, please reach out to the editor at [e-mail].

At the end of Chapter 3, the lyrics-trainer demo worked. That’s good, but in a way, that’s also a problem. We verified persistence the way developers often verify small browser features. We manually opened the page in a browser, went to the developer tools, clicked a button, changed a localStorage value in the console, refreshed, and watched what happened.

That was useful, but it’s not a test. It’s a demo.

That distinction matters, because a demo is the most expensive and most unreliable way to test an application. Most demos don’t verify edge cases or failure modes. They just run enough to see the system work, and since most developers want to see the system work, they often don’t bother to prod. I wrote a book about testing¹, so I’m hardly neutral about testing, but the point is that a demo proves the app worked once, while you were watching, while tests run automatically, checking their outputs against known results. A solid test suite has been a foundation of solid development for ...