Jest coverage diff

Use the action to get jest coverage diff for pull requests as a comment on the pull request. Helps the code reviewer to get the high level view of code coverage changes without leaving the pull request window.

Now with full Monorepo Support! 🎉

Features

• 📊 Beautiful, collapsible coverage reports
• 🏗️ Monorepo support - automatically discovers and compares coverage for all projects
• 📈 Weighted total coverage calculation across multiple projects
• 🆕 Highlights new projects
• 🎯 Shows only projects with changes
• 📁 File-level coverage details for each project
• ⚠️ Configurable thresholds to fail CI on coverage drops

Example Output

Summary

Metric	Before	After	Change
Lines	70.29%	69.53%	🟡 -0.76%
Statements	69.97%	69.13%	🟡 -0.84%
Functions	59.35%	56.85%	🟡 -2.50%
Branches	48.91%	47.39%	🟡 -1.52%

📦 Package Details

📦 backend/liquidity-service (🟡 -4.01%)

Package Summary

Metric	Before	After	Change
Lines	85.07%	81.06%	🟡 -4.01%
Statements	84.71%	80.46%	🟡 -4.25%
Functions	76.27%	69.49%	🟡 -6.78%
Branches	71.11%	61.11%	🟡 -10.00%

How It Works

The action is a pure comparison tool - it recursively searches for all coverage-summary.json files in the specified directories and generates a comprehensive diff report.

Typical Workflow

1. Run your tests and generate coverage for the current PR branch
2. Download baseline coverage from S3/artifact storage (using base branch SHA)
3. Action compares all projects and generates a beautiful diff comment
4. Optionally fails CI if coverage drops below threshold

Note: The action does NOT run tests or perform git operations. You must provide pre-generated coverage files in both directories.

Configuration

Inputs

Input	Description	Required	Default
accessToken	GitHub token for commenting on PR	No	${{ github.token }}
newCoveragePath	Path to new/current coverage directory	Yes	-
oldCoveragePath	Path to baseline coverage directory	Yes	-
useSameComment	Update existing comment instead of creating new ones	No	false
delta	Maximum allowed coverage drop per project (percentage)	No	100
total_delta	Maximum allowed total coverage drop (percentage)	No	null

Sample Workflow - Monorepo

name: Coverage Diff

on: pull_request

jobs:
  coverage:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      
      - name: Setup Node
        uses: actions/setup-node@v3
        with:
          node-version: '18'
      
      - name: Install dependencies
        run: npm ci
      
      # Generate coverage for current PR
      - name: Run tests with coverage
        run: npm run test:coverage
      
      # Download baseline coverage from S3
      - name: Download baseline coverage
        env:
          BASE_SHA: ${{ github.event.pull_request.base.sha }}
        run: |
          aws s3 sync s3://your-bucket/coverage/$BASE_SHA/ baseline/coverage/
      
      # Compare coverage
      - name: Coverage Diff
        uses: talkl/Jest-Coverage-Diff@master
        with:
          newCoveragePath: coverage
          oldCoveragePath: baseline/coverage
          useSameComment: true
          delta: 1
          total_delta: 0.5

Sample Workflow - Single Project

name: Coverage Diff

on: pull_request

jobs:
  coverage:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      
      - name: Setup Node
        uses: actions/setup-node@v3
        with:
          node-version: '18'
      
      - run: npm ci
      
      # Run tests and generate coverage
      - name: Generate current coverage
        run: npx jest --coverage --coverageReporters="json-summary" --coverageDirectory="./coverage"
      
      # Switch to base branch and generate baseline coverage
      - name: Generate baseline coverage
        run: |
          git fetch origin ${{ github.event.pull_request.base.ref }}
          git checkout origin/${{ github.event.pull_request.base.ref }}
          npm ci
          npx jest --coverage --coverageReporters="json-summary" --coverageDirectory="./baseline/coverage"
          git checkout -
      
      - name: Coverage Diff
        uses: talkl/Jest-Coverage-Diff@master
        with:
          newCoveragePath: coverage
          oldCoveragePath: baseline/coverage
          delta: 1

Monorepo Directory Structure

The action expects the following structure:

coverage/
├── apps/
│   ├── backend/
│   │   ├── liquidity-service/
│   │   │   └── coverage-summary.json
│   │   └── audit-logs-service/
│   │       └── coverage-summary.json
│   └── frontend/
│       └── coverage-summary.json
└── packages/
    ├── utils/
    │   └── coverage-summary.json
    └── components/
        └── coverage-summary.json

Each coverage-summary.json should follow the standard Jest coverage format.

Advanced Configuration

Delta Thresholds

• delta: Per-project threshold (e.g., 1 = fail if any project drops >1%)
• total_delta: Overall threshold (e.g., 0.5 = fail if total coverage drops >0.5%)

Notes

• The action works best with pull request events
• Projects that exist in baseline but not in new coverage are silently ignored
• New projects are highlighted with 🆕 but don't cause failures
• Only projects with actual changes are shown in the comment
• All details are collapsed by default for a clean view

License

MIT