Understanding Headless vs. Headed Modes in Playwright: A Guide for QA Automation Engineers / SDETs

As a Software Development Engineer in Test (SDET), understanding how to leverage headless and headed browser modes in Playwright can significantly impact the efficiency of your automated tests. In this article, we’ll explore these two modes, their pros and cons, and why headless mode is often preferred in Continuous Integration/Delivery (CI/CD) pipelines.

What Are Headless and Headed Modes?

• Headless Mode: The browser operates without a graphical user interface (GUI). In essence, it runs in the background, rendering the DOM and executing all operations without displaying anything on the screen.

• Headed Mode: The browser operates with a GUI, allowing you to visually see the browser as it navigates, interacts with elements, and executes tests.

Configuring Headless and Headed Modes in Playwright

In Playwright, switching between these modes is straightforward. You can control the mode by setting the headless property in the launch method of the browser.

Example:

import { chromium } from 'playwright';

(async () => {
    const browser = await chromium.launch({ headless: true }); // Headless mode
    const context = await browser.newContext();
    const page = await context.newPage();

    await page.goto('https://example.com');
    console.log(await page.title());

    await browser.close();
})();

Change headless: true to headless: false for headed mode.

Pros and Cons of Headless and Headed Modes

Headless Mode

Pros:

1. Performance: Faster execution as no GUI needs rendering.
2. Resource Efficiency: Consumes less CPU and memory, allowing for parallel execution of multiple tests.
3. Scalability: Ideal for CI/CD pipelines where multiple tests run simultaneously.

Cons:

1. Debugging Difficulty: Without visual feedback, debugging failures can be challenging. Screenshots and videos become essential for diagnosing issues.
2. False Positives/Negatives: Minor discrepancies might arise due to differences in rendering behavior compared to a GUI-enabled browser.

Headed Mode

Pros:

1. Debugging Ease: Provides a clear view of the browser’s actions, making it easier to identify issues during test execution.
2. Realistic Interactions: Useful for validating animations, transitions, and user interface behaviors that depend on visual elements.
3. Ideal for Automation and Debugging: Headed mode is especially good for scenarios where visual feedback is necessary to troubleshoot problems.

Cons:

1. Performance Overhead: Slower execution due to GUI rendering.
2. Resource Intensive: Requires more CPU and memory, which can limit parallel execution.

Why Headless Mode Works Better

1. Stealthier Execution: Headless mode often avoids triggering detection mechanisms because it mimics user interactions without rendering a GUI, reducing anomalies in behavior.
2. Fewer Visual Artifacts: Websites might flag elements like the absence of mouse movements or odd window dimensions in headed mode, whereas headless mode can replicate consistent, browser-like behavior.
3. Lower Overhead: Headless mode avoids rendering, meaning it can be more consistent and less prone to resource-related delays that could be flagged by a website.

Why Use Headless Mode in CI/CD Pipelines?

CI/CD pipelines prioritize speed, resource efficiency, and reliability. Headless mode aligns perfectly with these requirements:

1. Faster Execution: Tests run quicker without GUI rendering, reducing the total pipeline runtime.
2. Resource Optimization: Multiple headless browsers can run simultaneously on the same machine, maximizing resource utilization.
3. Non-Interactive Environments: CI/CD pipelines typically operate in server environments without display capabilities, making headless mode the default choice.

Best Practices for Using Headless Mode in CI/CD Pipelines

Enable Logging: Capture console logs to debug JavaScript errors and other issues.

page.on('console', msg => console.log(msg.text()));

Use Screenshots and Videos: Configure Playwright to capture screenshots or videos for failed tests.

await page.screenshot({ path: 'screenshot.png' });

Configure Timeouts: Set appropriate timeouts for elements to avoid false negatives caused by slow-loading pages.

await page.waitForSelector('#element', { timeout: 5000 });

Run Tests Locally in Headed Mode: Use headed mode for local debugging and headless mode for pipeline execution. Playwright’s built-in UI mode can help during test creation and debugging by visualizing test runs:

npx playwright test --ui

Use the Same Browser Version: Ensure consistency by using the same browser version locally and in CI/CD to avoid discrepancies.

Debugging Tips for Headless Mode

Even in headless mode, Playwright offers robust debugging capabilities:

• Record Traces: Use the trace viewer to capture and replay test actions step by step.

await context.tracing.start({ screenshots: true, snapshots: true });
// Run your test steps
await context.tracing.stop({ path: 'trace.zip' });

Conclusion

Understanding the trade-offs between headless and headed modes is crucial for SDETs working with Playwright. While headed mode is invaluable for debugging and local development, headless mode reigns supreme in CI/CD pipelines due to its speed and resource efficiency. By adopting best practices like logging, screenshots, and trace recording, you can ensure robust and reliable automation in headless environments.

Comments

[rcanelav]

I didn't know about taking screenshots and videos with playwright!! Really useful, thanks!!