🧪 Add tests for generateDemoIsland

[Ap-0007]

🎯 What: The testing gap addressed
The generateDemoIsland function in lib/island-engine.ts lacked tests. This function wraps generateIslandGrid with demo activity and it is now fully covered to ensure behavior remains correct.

📊 Coverage: What scenarios are now tested

• The output grid having valid dimensions and structure.
• Default theme and explicitly specified themes ('tropical', 'winter', 'sakura', 'spooky').
• Determinism (ensuring the same inputs result in identical outputs).
• Validation of tile emojis falling into expected themes and intensity within bounds.

✨ Result: The improvement in test coverage
We now have solid, fast unit tests covering the demo island generation.
Also formalized test execution via npm test.

---

PR created automatically by Jules for task 3172921071050631014 started by @Ap-0007

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
side_pro	Ready	Preview, Comment	May 18, 2026 1:05pm