How to Run Playwright Tests in Parallel

Have you ever faced the frustration of slow test execution, especially when running large Playwright test suites?

I certainly have.

In my experience, running tests sequentially often wastes a significant portion of development time, sometimes as much as 30 percent, waiting for feedback from CI.

This delay not only slows down development but also impacts the speed at which features can be shipped.

Parallel testing promises to solve this problem by reducing test execution time. But setting it up correctly with Playwright can be tricky.

This article explores how to set up and optimize parallel test execution in Playwright, covering key configurations, best practices, and troubleshooting tips.

Why Parallel Testing is Essential?

Parallel testing is a powerful strategy for optimizing test execution, especially when dealing with large and complex test suites.

Running tests sequentially can lead to significant delays, particularly as the number of tests increases. By executing tests in parallel, you can drastically reduce overall testing time, enabling faster feedback loops and speeding up the development process.

Key benefits of parallel testing include:

• Faster feedback: Run multiple tests at once, reducing the time it takes to get results from your CI/CD pipeline.
• Improved efficiency: Test suites that might take hours to run sequentially can be completed in a fraction of the time.
• Better scalability: As your application grows and your test suite expands, parallel testing allows your testing infrastructure to scale easily, handling larger loads without slowing down.
• Cost-effectiveness: By reducing test runtime, parallel testing optimizes resource usage, making your testing process more efficient and reducing the cost of long-running CI jobs.

In short, parallel testing ensures quicker validation of code changes, better resource utilization, and improved developer productivity, all of which are critical for agile development and continuous integration.

As your testing needs grow, especially when scaling test execution across multiple browsers and devices, managing parallel tests can become more complex.

BrowserStack Automate helps streamline this by running Playwright tests in parallel on real browsers and devices in the cloud, freeing up local resources and ensuring broader test coverage.

With BrowserStack, you can effortlessly scale parallel testing while maintaining consistent test execution across environments.

How Playwright Handles Parallel Execution

Playwright supports parallel test execution out of the box, allowing tests to run concurrently, reducing overall execution time. It achieves this through worker processes and isolated browser contexts, ensuring tests do not interfere with each other.

Key Features of Playwright Parallel Execution

1. Parallel Execution with Workers

Playwright runs tests in separate worker processes, enabling parallel execution without waiting for each test to finish. This reduces test runtime significantly.

2. Test Parallelization

Use test.parallel() and test.describe.parallel() to group and run tests concurrently.

test.describe.parallel(‘Parallel tests’, () => {

test(‘Test 1’, async ({ page }) => { … });

test(‘Test 2’, async ({ page }) => { … });

});

3. Isolated Browser Contexts

Each parallel test runs in its own isolated browser context, ensuring no shared state or interference between tests.

4. Configuring Parallelism

Control parallel execution by setting the number of workers in the playwright.config.ts file.

module.exports = {

workers: 4, // Run tests in 4 parallel workers

};

Setting Up Parallel Execution in Playwright

Setting up parallel execution in Playwright is straightforward and involves configuring a few settings. By running tests concurrently, you can significantly reduce overall test execution time and optimize your CI pipeline.

1. Install Playwright and Set Up Your Test Environment

Ensure Playwright is installed and your test environment is set up:

npm install playwright

Create a basic Playwright test suite to get started, ensuring tests are isolated and independent for parallel execution.

2. Configure Parallel Execution in playwright.config.ts

In the playwright.config.ts file, you can configure the number of workers (parallel test processes) to run.

Example configuration:

module.exports = {

workers: 4, // Run 4 tests in parallel

};

This configures Playwright to run tests in 4 parallel worker processes. You can adjust this number based on the available resources (CPU, memory).

3. Use test.parallel() and test.describe.parallel() for Grouping Tests

Playwright provides test.parallel() and test.describe.parallel() to execute tests concurrently. These methods allow you to group tests or individual test cases to run in parallel.

Example of grouping tests:

test.describe.parallel(‘Parallel tests’, () => {

test(‘Test 1’, async ({ page }) => {

await page.goto(‘https://example.com’);

await expect(page).toHaveTitle(‘Example Domain’);

});

test(‘Test 2’, async ({ page }) => {

await page.goto(‘https://example.com’);

await expect(page).toHaveTitle(‘Example Domain’);

});

});

4. Consider Browser Contexts for Test Isolation

Each test should run in its own browser context to avoid shared state. Playwright ensures this by creating a separate browser context for each parallel test, providing an isolated environment.

Example of creating independent contexts:

const context1 = await browser.newContext();

const context2 = await browser.newContext();

5. Run Tests in Parallel on CI/CD

In your CI/CD pipeline, ensure that your infrastructure supports parallel test execution. Most CI tools like Jenkins, GitHub Actions, and GitLab support parallel execution by default.

Make sure to configure your CI settings to allocate enough resources for the specified number of parallel tests.

Running Playwright Tests in Parallel with Test Runners

Playwright can be integrated with popular test runners like Playwright Test, Jest, or Mocha to run tests in parallel. These test runners allow you to execute Playwright tests concurrently, speeding up your feedback cycle and making your test suite more efficient.

1. Using Playwright Test Runner for Parallel Execution

Playwright’s built-in test runner supports parallel execution natively, making it the easiest way to run tests in parallel.

Key steps to set up parallel execution

1. Install Playwright Test runner

npm install @playwright/test

2. Configure the workers option in the playwright.config.ts file to define the number of parallel workers (test processes).

Example:

// playwright.config.ts

module.exports = {

workers: 4, // Run 4 tests in parallel

};

3. Use test.parallel() to run specific tests in parallel.

Example:

test.describe.parallel(‘Parallel tests’, () => {

test(‘Test 1’, async ({ page }) => {

await page.goto(‘https://example.com’);

await expect(page).toHaveTitle(‘Example Domain’);

});

test(‘Test 2’, async ({ page }) => {

await page.goto(‘https://example.com’);

await expect(page).toHaveTitle(‘Example Domain’);

});

});

This configuration runs both tests in parallel, reducing the total runtime of your test suite.

2. Using Jest for Parallel Playwright Testing

Jest can also be used with Playwright for parallel test execution. Jest runs tests concurrently by default, so you can take advantage of this feature with minimal setup.

Steps to set up Jest with Playwright

1. Install necessary dependencies

npm install –save-dev jest @playwright/test

2. Create a jest.config.js file and configure it for parallel execution by setting the maxWorkers option.

Example:

// jest.config.js

module.exports = {

maxWorkers: ‘50%’, // Use up to 50% of available CPU cores for parallel tests

};

3. Write Playwright tests using Jest syntax

const { chromium } = require(‘playwright’);

describe(‘Playwright Tests’, () => {

let browser;

let page;
beforeAll(async () => {

browser = await chromium.launch();

page = await browser.newPage();

});
afterAll(async () => {

await browser.close();

});
test(‘Test 1’, async () => {

await page.goto(‘https://example.com’);

expect(await page.title()).toBe(‘Example Domain’);

});
test(‘Test 2’, async () => {

await page.goto(‘https://example.com’);

expect(await page.title()).toBe(‘Example Domain’);

});

});

3. Using Mocha for Parallel Playwright Testing

Mocha can also be used to run Playwright tests in parallel with a few configurations.

Steps to set up Mocha

1. Install Mocha and Playwright

npm install –save-dev mocha @playwright/test

2. Mocha itself does not support parallel test execution directly, but you can use the mocha-parallel-tests module to enable parallelism.

npm install –save-dev mocha-parallel-tests

3. Update your test script to run tests in parallel

{

“scripts”: {

“test”: “mocha-parallel-tests”

}

}

4. Write your Playwright test cases using Mocha syntax

const { chromium } = require(‘playwright’);

describe(‘Parallel Playwright Tests’, () => {

let browser;

let page;
before(async () => {

browser = await chromium.launch();

page = await browser.newPage();

});
after(async () => {

await browser.close();

});
it(‘Test 1’, async () => {

await page.goto(‘https://example.com’);

expect(await page.title()).toBe(‘Example Domain’);

});
it(‘Test 2’, async () => {

await page.goto(‘https://example.com’);

expect(await page.title()).toBe(‘Example Domain’);

});

});

4. Running Playwright Tests in Parallel on CI/CD Platforms

Integrating parallel testing with CI/CD platforms (e.g., Jenkins, GitHub Actions, GitLab CI) is straightforward once the parallel execution is set up. These platforms support parallel jobs out of the box, allowing you to distribute the test execution across multiple agents or containers.

Example for GitHub Actions:

name: Playwright Tests

on: [push]
jobs:

run-tests:

runs-on: ubuntu-latest

strategy:

matrix:

browser: [firefox, chromium, webkit]

steps:

– name: Checkout code

uses: actions/checkout@v2
– name: Set up Node.js

uses: actions/setup-node@v2

with:

node-version: ’14’
– name: Install dependencies

run: npm install
– name: Run Playwright Tests

run: npm test

This configuration will run tests in parallel on multiple browsers (Chromium, Firefox, WebKit) in different CI jobs, further speeding up the overall testing process.

Managing Test Dependencies in Parallel Execution

When running tests in parallel, managing dependencies becomes critical to ensure that tests do not interfere with one another and produce consistent, reliable results.

Since parallel tests run simultaneously in separate worker processes or browser contexts, any shared state or data can lead to race conditions or flaky tests.

Here’s how to effectively manage dependencies when executing tests in parallel:

1. Ensure Test Independence

• Isolate tests: Each test should be independent and not rely on the state of others. Avoid sharing global variables or mutable state between tests.
• Use unique data: If tests require data (like login credentials or session tokens), make sure each test has its own set to avoid conflicts.

Example:

test(‘Test 1 – Login’, async ({ page }) => {

await page.goto(‘https://example.com/login’);

await page.fill(‘input[name=”username”]’, ‘user1’);

await page.fill(‘input[name=”password”]’, ‘password1’);

await page.click(‘button[type=”submit”]’);

expect(await page.url()).toBe(‘https://example.com/dashboard’);

});

2. Use Browser Contexts for Isolation

Separate browser contexts: Playwright allows tests to run in isolated browser contexts using browser.newContext(). This ensures no shared state (like cookies, local storage, or session data) between tests.

Example:

const context1 = await browser.newContext(); // Independent context

const page1 = await context1.newPage();

await page1.goto(‘https://example.com’);

const context2 = await browser.newContext(); // Another independent context

const page2 = await context2.newPage();

await page2.goto(‘https://example.com’);

3. Use Test Hooks for Setup and Teardown

Global setup and teardown: Use beforeAll() and afterAll() hooks for setup and teardown tasks that should only run once for all tests in a suite. This prevents redundancy and improves performance.

Example:

let browser;

beforeAll(async () => {

browser = await chromium.launch();

});
afterAll(async () => {

await browser.close();

});
test(‘Test 1’, async () => { /* Test code */ });

test(‘Test 2’, async () => { /* Test code */ });

Individual test setup: Use beforeEach() and afterEach() hooks to initialize things like page navigation or element state before and after each test. This ensures that each test starts with a clean slate.

4. Handle Shared Resources Carefully

Database or API calls: If tests interact with shared databases or APIs, use test-specific data or mock responses to prevent data conflicts. Mocking external services can be useful for isolating tests and avoiding race conditions.

Example using a mock:

test(‘Test API call’, async ({ page }) => {

await page.route(‘**/api/**’, route => route.fulfill({ status: 200, body: ‘{“key”: “value”}’ }));

await page.goto(‘https://example.com’);

// Test assertions here

});

Best Practices for Running Playwright Tests in Parallel

Running Playwright tests in parallel can significantly speed up your testing process, but it requires careful planning to ensure tests are stable, reliable, and efficient. To get the most out of parallel test execution, follow these best practices:

• Isolate Tests: Ensure tests are independent by avoiding shared state (e.g., cookies, local storage). Use Playwright’s newContext() to create isolated environments for each test.
• Limit Parallelism: Control the number of parallel tests based on your system’s available resources (CPU, memory). Adjust the workers setting in playwright.config.ts to avoid overload.
• Use Headless Mode: Run tests in headless mode to reduce resource consumption and improve test execution speed, as no graphical interface is required for browser operations.
• Group Related Tests: Use test.describe.parallel() to group similar tests together, ensuring that related tests run in parallel, optimizing resource allocation and reducing overhead.
• Handle Flaky Tests: Set up automatic retries for flaky tests using Playwright’s retries configuration. This helps avoid failures caused by intermittent issues and ensures stability.
• Optimize Setup/Teardown: Use beforeAll() and afterAll() hooks to set up and clean up shared resources once per suite, rather than before/after each test, reducing redundant work.
• Adjust Timeouts: Increase timeouts slightly to account for variability in test execution time when running in parallel, especially in CI environments with varying load conditions.
• Use CI/CD for Parallel Execution: Integrate parallel test execution into your CI/CD pipeline (e.g., Jenkins, GitHub Actions) to run tests across multiple agents or containers, improving scalability and speed.
• Consolidate Test Reports: Aggregate test results using reporting tools like JUnit or Allure to combine outputs from parallel tests into one comprehensive report, simplifying analysis and debugging.

Scale Your Parallel Testing with BrowserStack Automate

As your Playwright test suite grows, running tests in parallel on your local machine or in a single environment may not be sufficient. BrowserStack Automate allows you to scale your parallel testing effortlessly by running tests on real browsers and devices in the cloud.

This not only expands your test coverage but also improves efficiency by executing tests across multiple environments simultaneously.

Key Benefits of Scaling with BrowserStack Automate

• Cross-Browser and Cross-Device Coverage: Run your Playwright tests on a wide variety of real desktop browsers, mobile browsers, and devices, ensuring complete coverage for your application across different platforms.
• Seamless Parallel Execution: BrowserStack allows you to run hundreds of Playwright tests in parallel, speeding up test execution and enabling faster feedback. This reduces the time spent waiting for test results, improving your development velocity.
• No Infrastructure Overhead: With BrowserStack Automate, there’s no need to worry about managing or scaling your own testing infrastructure. BrowserStack’s cloud infrastructure handles scaling automatically, so you can focus on writing and maintaining tests.
• Real User Conditions: Tests are run on real devices and browsers, providing a more accurate representation of how your application performs in production, compared to simulated environments.
• Easy Integration with CI/CD Pipelines: Integrate BrowserStack Automate with your CI/CD pipeline effortlessly. BrowserStack supports popular CI tools like Jenkins, GitHub Actions, and GitLab, making it easy to scale parallel testing directly within your existing workflows.

By leveraging BrowserStack Automate for parallel testing, you can scale your testing infrastructure seamlessly, ensuring faster and more reliable tests without the need for managing complex environments or additional resources.

This approach accelerates your feedback loop, improves test coverage, and allows you to focus more on development rather than infrastructure management.

Talk to an Expert

Conclusion

Parallel testing is an essential strategy for speeding up Playwright test execution, especially as your test suite grows. By running tests concurrently, you can reduce test execution time, improve feedback speed, and scale your testing process efficiently. However, achieving optimal parallel execution requires careful setup and management, including test isolation, resource optimization, and proper configuration.

While local parallel testing is effective for smaller projects, scaling to larger test suites with broader browser and device coverage requires leveraging cloud-based solutions like BrowserStack Automate. By using BrowserStack, you can seamlessly run Playwright tests in parallel on real browsers and devices, improving test accuracy and scalability without the burden of managing infrastructure.

With the right configuration, best practices, and tools in place, parallel testing can drastically enhance your testing workflow, making it faster, more reliable, and capable of supporting modern development cycles.

Try BrowserStack Now

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• Page Object Model in Playwright
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• Understanding Playwright Assertions
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