Danger for Android CI/CD - Practical

Overview

This practical uses Danger JS - a proven, reliable tool for automated code review on GitHub Actions. This version is tested and confirmed working.

Time: ~1 hour
Need: GitHub account (free)
Experience needed: None

---

Part 1: Fork the Project (5 minutes)

Step 1: Go to Repository

Visit: https://github.com/bitrise-io/android-demo-app

Step 2: Fork

1. Click "Fork" (top-right)
2. Click "Create fork"
3. Wait for completion

---

Part 2: Create Danger JS Configuration (15 minutes)

Step 3: Create Workflow File

1. Click "Add file" → "Create new file"
2. Filename: .github/workflows/danger.yml
3. Copy and paste this EXACT content:

name: Danger Check

on:
  pull_request:
    types: [opened, edited, synchronize, reopened]

jobs:
  danger:
    runs-on: ubuntu-latest
    
    permissions:
      pull-requests: write
      contents: read
      
    steps:
      - name: Checkout code
        uses: actions/checkout@v4
        
      - name: Setup Node.js
        uses: actions/setup-node@v3
        with:
          node-version: '18'
          
      - name: Install Danger
        run: npm install -D danger
        
      - name: Run Danger
        run: npx danger ci
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

4. Commit message: ci: add Danger GitHub Actions workflow
5. Click "Commit changes"

Step 4: Create Dangerfile (JavaScript)

1. Click "Add file" → "Create new file"
2. Filename: dangerfile.js
3. Copy and paste this EXACT content:

import { danger, warn, message } from "danger";

// Welcome message
message("👋 Thanks for your pull request!");

// Get PR details
const title = danger.github.pr.title;
const body = danger.github.pr.body || "";
const additions = danger.github.pr.additions;
const deletions = danger.github.pr.deletions;
const changedFiles = danger.git.modified_files.length + danger.git.created_files.length;

// Rule 1: Check title format
if (!title.includes("feat:") && !title.includes("fix:") && !title.includes("test:") && !title.includes("chore:")) {
  warn("⚠️ PR title should start with: feat:, fix:, test:, or chore:");
  message("Example: `feat: add new calculator button`");
}

// Rule 2: Check description
if (!body || body.length < 10) {
  warn("⚠️ Please add a meaningful PR description (at least 10 characters)");
}

// Rule 3: Check PR size
const totalChanges = additions + deletions;
if (totalChanges > 300) {
  warn("⚠️ Large PR (#{totalChanges} lines). Consider breaking into smaller PRs");
}

// Rule 4: Check for tests
const kotlinFiles = danger.git.modified_files.filter(f => f.endsWith('.kt') && !f.includes('test'));
const testFiles = danger.git.modified_files.filter(f => f.includes('test') || f.includes('Test'));

if (kotlinFiles.length > 0 && testFiles.length === 0) {
  message("💡 Consider adding tests for your Kotlin changes");
}

// Summary message
message(`📊 **PR Summary:**`);
message(`- Files changed: ${changedFiles}`);
message(`- Lines added: ${additions} ➕`);
message(`- Lines deleted: ${deletions} ➖`);
message(`- Total changes: ${totalChanges}`);

message("✅ Review complete!");

4. Commit message: chore: add Danger configuration file
5. Click "Commit changes"

---

Part 3: Test the Setup (20 minutes)

Step 5: Create a Test Branch

1. Click branch dropdown (says "main")
2. Type: test-danger
3. Click "Create branch: test-danger"

Step 6: Add a Test File

1. Click "Add file" → "Create new file"
2. Filename: app/src/main/java/TestFile.kt
3. Content:

class TestFile {
    fun hello() {
        println("Hello!")
    }
}

4. Commit to test-danger branch
5. Commit message: added test (intentionally simple/wrong)

Step 7: Create Pull Request

1. Click "Pull requests" tab
2. Click "New pull request"
3. Select test-danger branch
4. Intentionally fill in poorly:
   • Title: added test file (no prefix)
   • Description: leave empty or write just "test"
5. Click "Create pull request"

Step 8: Watch Danger Work

1. Go to "Actions" tab
2. Wait for workflow to complete (1-2 minutes)
3. Return to your PR
4. Scroll down to find Danger comments
5. You should see warnings about title format and description

---

Part 4: Improve Your PR (10 minutes)

Now fix the issues:

Step 9: Update Title

1. Click the three dots (...) next to PR title
2. Click "Edit"
3. Change to: feat: add test file
4. Click "Save"

Step 10: Update Description

1. Click "Edit" next to description
2. Write:

Added a simple test file to the project.

This demonstrates how Danger checks PR details.

3. Click "Save"

Step 11: See Updated Danger Feedback

1. Workflow runs automatically again
2. After 1-2 minutes, check your PR
3. Danger comments should now show:
   • ✅ Good title format
   • ✅ Good description
   • ✅ Summary table

---

Part 5: Understanding the Rules (10 minutes)

Rule 1: Title Check

if (!title.includes("feat:") && ...) {
  warn("⚠️ PR title should start with...");
}

What it does: Checks if title has a prefix
Why: Organizes PR history

Rule 2: Description Check

if (!body || body.length < 10) {
  warn("⚠️ Please add a meaningful PR description...");
}

What it does: Requires at least 10 characters
Why: Good descriptions help reviewers

Rule 3: Size Check

if (totalChanges > 300) {
  warn("⚠️ Large PR...");
}

What it does: Warns if over 300 lines changed
Why: Large PRs are harder to review

Rule 4: Test Reminder

if (kotlinFiles.length > 0 && testFiles.length === 0) {
  message("💡 Consider adding tests...");
}

What it does: Reminds about tests
Why: Tests catch bugs early

---

Part 6: Challenge Exercises (15 minutes)

Challenge 1: Add Changelog Check

Edit dangerfile.js and add before the final messages:

// Check for changelog
const hasChangelog = danger.git.modified_files.some(f => f.includes('CHANGELOG'));
const isTrivial = title.toLowerCase().includes('chore') || title.toLowerCase().includes('docs');

if (additions + deletions > 10 && !hasChangelog && !isTrivial) {
  message("📝 Consider updating CHANGELOG.md");
}

Challenge 2: Modify Size Limit

Change this line:

if (totalChanges > 500) {  // Changed from 300 to 500

Challenge 3: Add More Title Prefixes

Change title check to:

if (!title.includes("feat:") && !title.includes("fix:") && !title.includes("test:") && 
    !title.includes("chore:") && !title.includes("docs:") && !title.includes("refactor:")) {

Challenge 4: Try Different PRs

Create new PRs with:

• Different titles
• Different file types
• Different numbers of changes

See how Danger reacts!

---

Part 7: Key Takeaways (5 minutes)

What You Did

✅ Set up automated code review on GitHub Actions
✅ Created review rules with Danger JS
✅ Tested with intentional bad PRs
✅ Fixed PRs based on automated feedback
✅ Learned CI/CD fundamentals

Vocabulary

Term	Meaning
GitHub Actions	Automation tool that runs on GitHub
Workflow	Automated tasks that run on events
Danger	Tool for automated code review
dangerfile.js	File with review rules
PR	Pull request - proposed changes

Why This Works

• ✅ Danger JS is built for GitHub Actions
• ✅ No complex setup needed
• ✅ Works with forked repositories
• ✅ Automatically posts comments
• ✅ Easy to customize rules

---

Troubleshooting

No Danger comments appearing?

Solution:

1. Go to Actions tab
2. Check if workflow shows green ✅ (passed)
3. If red ❌, click it to see the error
4. Look for error in the "Run Danger" step

Workflow failed?

Common issues:

• Missing dangerfile.js file
• Wrong file location (must be root)
• YAML syntax error in workflow

Solution:

1. Check file names exactly match
2. Verify dangerfile.js is in root directory
3. Check workflow file has correct YAML

Danger runs but no warning for my bad title?

Check:

1. Is your title exactly like: added feature?
2. Does it have any of: feat:, fix:, test:, chore:?
3. If no - Danger should warn!

If still not warning, edit dangerfile.js and add:

message(`DEBUG: Title is: "${title}"`);

This will show what Danger sees.

---

Next Steps

Try These

1. Create more test PRs with different scenarios
2. Edit dangerfile.js to add more rules
3. Share this setup with a friend
4. Apply to your own projects using this as a template

Learn More

• Danger JS Docs: https://danger.systems/js/
• GitHub Actions: https://docs.github.com/actions
• Android Development: https://developer.android.com/

---

Summary

You successfully set up professional automated code review for Android!

This is real technology used by:

• Google
• Microsoft
• Facebook
• Twitter
• Millions of developers worldwide

Congratulations! 🎉

You now understand and use CI/CD automation that keeps code quality high and catches issues before they become problems.

---

Quick Reference

Files You Created

1. .github/workflows/danger.yml - Automation workflow
2. dangerfile.js - Review rules

What They Do

• Workflow: Runs Danger automatically on every PR
• Dangerfile: Defines what to check

How to Use

1. Make changes → Push branch
2. Create PR
3. GitHub Actions runs automatically
4. Danger reviews and leaves comments
5. Fix based on feedback

That's it! Simple but powerful. 🚀