What is test sharding in Playwright and how does it work?

Total: 400 tests

Shard 1/4 → runs tests 1-100
Shard 2/4 → runs tests 101-200
Shard 3/4 → runs tests 201-300
Shard 4/4 → runs tests 301-400

All shards run simultaneously → 4x speedup!

# Machine 1 of 4
npx playwright test --shard=1/4

# Machine 2 of 4
npx playwright test --shard=2/4

# Machine 3 of 4
npx playwright test --shard=3/4

# Machine 4 of 4
npx playwright test --shard=4/4

# .github/workflows/playwright.yml
name: Playwright Tests

jobs:
  test:
    timeout-minutes: 60
    runs-on: ubuntu-latest

    strategy:
      fail-fast: false
      matrix:
        shardIndex: [1, 2, 3, 4]
        shardTotal: [4]

    steps:
      - uses: actions/checkout@v4

      - uses: actions/setup-node@v4
        with:
          node-version: 20

      - name: Install dependencies
        run: npm ci

      - name: Install Playwright browsers
        run: npx playwright install --with-deps

      - name: Run tests (shard ${{ matrix.shardIndex }}/${{ matrix.shardTotal }})
        run: npx playwright test --shard=${{ matrix.shardIndex }}/${{ matrix.shardTotal }}

      # Upload each shard's results for merging
      - name: Upload shard report
        if: always()
        uses: actions/upload-artifact@v4
        with:
          name: playwright-report-${{ matrix.shardIndex }}
          path: playwright-report/
          retention-days: 30

  merge-reports:
    needs: test
    if: always()
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with: { node-version: 20 }
      - run: npm ci

      - name: Download all shard reports
        uses: actions/download-artifact@v4
        with:
          path: all-blob-reports
          pattern: playwright-report-*

      - name: Merge reports
        run: npx playwright merge-reports --reporter html ./all-blob-reports

      - name: Upload combined report
        uses: actions/upload-artifact@v4
        with:
          name: playwright-report-combined
          path: playwright-report/

// playwright.config.ts
export default defineConfig({
  workers: 4,           // 4 parallel workers per shard
  fullyParallel: true,
});