What is the difference between sharding and using workers in @playwright/test?

Answer

You can run your tests in parallel using either sharding or workers in @playwright/test.

Sharding splits your test suite into smaller subsets, or shards, each running on a separate machine or process. This is great for distributing the workload across multiple machines and speeding up large test suites. However, it requires additional setup and coordination.

// Example of sharding in @playwright/test
// This is a conceptual example and may not work as-is
const shard = process.env.SHARD || '0';
const totalShards = process.env.TOTAL_SHARDS || '1';

// In your test file
test.describe.serial(`Shard ${shard} of ${totalShards}`, () => {
  // Your tests here
});

Workers, on the other hand, run tests concurrently within a single machine or process. Each worker process is independent and starts its own browser instance. You can control the number of workers using the --workers command line option or workers configuration option in the playwright.config.ts file.

// Example of using workers in @playwright/test
import { PlaywrightTestConfig } from '@playwright/test';

const config: PlaywrightTestConfig = {
  // Other config options...
  workers: 4, // Number of worker processes
};

export default config;

Workers simplify setup as there's no need for distributing tests across different machines. However, they can't share state or global variables.

So, whether you choose sharding or workers depends on your specific needs. If you have multiple machines, sharding could be a good option. If you're running tests within a single machine or process, workers might be simpler.