Parallel Test Execution with Sharding

Advanced15 min

Scale Playwright test suites by splitting tests across multiple CI machines using sharding for dramatically faster feedback loops.

Prerequisites

-Playwright test suite with many tests
-GitHub Actions or similar CI with matrix support

Steps

Run tests with sharding locally

Split test files across multiple shards for parallel execution.

$ npx playwright test --shard=1/3

Sharding splits test files, not individual tests. Use --shard=N/M where N is the shard index (1-based) and M is the total number of shards.

Configure CI matrix for sharding

Set up GitHub Actions to run shards in parallel across machines.

$ cat > .github/workflows/playwright-sharded.yml << 'EOF' name: Playwright Sharded on: [push, pull_request] jobs: test: runs-on: ubuntu-latest strategy: fail-fast: false matrix: shard: [1/4, 2/4, 3/4, 4/4] steps: - uses: actions/checkout@v4 - uses: actions/setup-node@v4 with: node-version: 20 cache: npm - run: npm ci - run: npx playwright install --with-deps chromium - run: npx playwright test --shard=${{ matrix.shard }} --project=chromium - uses: actions/upload-artifact@v4 if: ${{ !cancelled() }} with: name: blob-report-${{ strategy.job-index }} path: blob-report/ merge-reports: if: ${{ !cancelled() }} needs: test runs-on: ubuntu-latest steps: - uses: actions/checkout@v4 - uses: actions/setup-node@v4 with: node-version: 20 cache: npm - run: npm ci - uses: actions/download-artifact@v4 with: path: all-blob-reports pattern: blob-report-* merge-multiple: true - run: npx playwright merge-reports --reporter html ./all-blob-reports - uses: actions/upload-artifact@v4 with: name: playwright-report path: playwright-report/ EOF

Configure blob reporter for shard merging

Use the blob reporter to collect results from each shard for merging.

$ cat << 'EOF' // playwright.config.ts reporter: process.env.CI ? [['blob'], ['github']] : [['html']], EOF

Configure parallel workers per shard

Tune the number of parallel workers within each shard.

$ cat << 'EOF' // playwright.config.ts fullyParallel: true, workers: process.env.CI ? 2 : undefined, EOF

Each shard runs its own set of workers. With 4 shards and 2 workers each, you get 8 parallel test executions across your CI cluster.

Full Script

full-script.sh

#!/bin/bash
# Playwright Sharding Test
set -euo pipefail

TOTAL_SHARDS=${1:-4}

echo "=== Playwright Sharding Test ==="
echo "Total shards: $TOTAL_SHARDS"
echo ""

# Estimate test distribution
TOTAL_TESTS=$(npx playwright test --list 2>/dev/null | grep -c 'test' || echo "unknown")
echo "Total tests: $TOTAL_TESTS"

echo ""
echo "=== Running Each Shard ==="
for i in $(seq 1 "$TOTAL_SHARDS"); do
  echo ""
  echo "--- Shard $i/$TOTAL_SHARDS ---"
  TESTS_IN_SHARD=$(npx playwright test --shard="$i/$TOTAL_SHARDS" --list 2>/dev/null | grep -c 'test' || echo "?")
  echo "Tests in shard: $TESTS_IN_SHARD"
done

echo ""
echo "=== CI Matrix Configuration ==="
echo "Add to your workflow:"
echo "  strategy:"
echo "    matrix:"
echo -n "      shard: ["
for i in $(seq 1 "$TOTAL_SHARDS"); do
  [ $i -gt 1 ] && echo -n ", "
  echo -n ""$i/$TOTAL_SHARDS""
done
echo "]"

FAQ

Discussion

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#!/bin/bash # Playwright Sharding Test set -euo pipefail TOTAL_SHARDS=${1:-4} echo "=== Playwright Sharding Test ===" echo "Total shards: $TOTAL_SHARDS" echo "" # Estimate test distribution TOTAL_TESTS=$(npx playwright test --list 2>/dev/null | grep -c 'test' || echo "unknown") echo "Total tests: $TOTAL_TESTS" echo "" echo "=== Running Each Shard ===" for i in $(seq 1 "$TOTAL_SHARDS"); do echo "" echo "--- Shard $i/$TOTAL_SHARDS ---" TESTS_IN_SHARD=$(npx playwright test --shard="$i/$TOTAL_SHARDS" --list 2>/dev/null | grep -c 'test' || echo "?") echo "Tests in shard: $TESTS_IN_SHARD" done echo "" echo "=== CI Matrix Configuration ===" echo "Add to your workflow:" echo " strategy:" echo " matrix:" echo -n " shard: [" for i in $(seq 1 "$TOTAL_SHARDS"); do [ $i -gt 1 ] && echo -n ", " echo -n ""$i/$TOTAL_SHARDS"" done echo "]"