Parallel Jest Runner

Run Jest tests in parallel shards for faster execution and improved performance.

Overview

Parallel Jest Runner is a utility for running Jest tests in parallel across multiple shards to significantly reduce test execution time in large projects. It handles test distribution, coverage reporting, and error aggregation automatically.

Features

• Parallel Test Execution: Split tests into configurable shards for faster runs
• Coverage Reporting: Automatically merges coverage reports from all shards
• Smart Threshold Detection: Extracts coverage thresholds from your Jest config
• Detailed Error Reporting: Provides comprehensive failure summaries
• Configurable: Customize shards, memory limits, and more

Installation

npm install --save-dev parallel-jest-runner

Usage

Command Line

npx parallel-jest-runner

Options

• -s, --shards <number> - Number of shards to split tests into (default: 12)
• -m, --memory <number> - Memory size in MB for Node process (default: 12288)
• -w, --workers <number> - Max workers per shard (default: 1)
• -d, --dir <path> - Working directory (default: current directory)
• -a, --args <string> - Additional Jest arguments

Programmatic API

import { runParallelTests } from 'parallel-jest-runner';

async function runTests() {
  const result = await runParallelTests({
    numShards: 8,
    memorySize: 8192,
    maxWorkers: 2,
    workingDir: './my-project',
    additionalJestArgs: ['--bail']
  });
  
  console.log('Tests passed:', result.success);
  console.log('Test suites passed:', result.testSuitesPassed);
  console.log('Tests passed:', result.testsPassed);
}

runTests();

Benefits

• Faster CI Builds: Dramatically reduces test execution time
• Resource Optimization: Better utilization of multi-core systems
• Simplified Coverage: Handles coverage merging automatically
• Improved Reporting: Detailed failure information aggregated from all shards

Requirements

• Node.js 14 or higher
• Jest 26 or higher

License

MIT