A Complete Guide to Headless Browser Testing

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Over my decade-plus in app and browser testing, headless testing has emerged as a game-changing technique for modern QA teams. But what exactly is it? And is it relevant for organizations struggling with slow, flaky UI tests?

In this comprehensive 2500+ word guide, we’ll cover everything important about headless browsers and headless browser testing that testers should know.

Understanding Headless Browser Testing

Headless browser testing is the method of programatically controlling a browser without rendering the user interface (UI). This allows simulating user interactions and testing web apps faster and more stably.

Instead of a visible display, headless browsers work via command line interfaces and APIs. So you can navigate pages, enter data, execute JavaScript, submit forms etc. without actually seeing what’s happening.

For example, here is sample Puppeteer code to search on Google Headless:

// launch headless chrome
const browser = await puppeteer.launch();

// open blank page
const page = await browser.newPage(); 

// set viewport size  
await page.setViewport({width: 1280, height: 800})

// navigate to google.com
await page.goto(‘https://www.google.com/‘);  

// type search phrase  
await page.type(‘.gLFyf‘, ‘BrowserStack‘);    

// click search button
await page.click(‘input[type="submit"]‘); 

// assert page title contains results 
expect(await page.title()).toContain(‘BrowserStack‘);   

// close browser
await browser.close();

Even without any visible UI, Puppeteer can programmatically drive Chrome to load web pages, enter text, click elements and make assertions – all in a headless state.

Other popular automation libraries like Playwright and Selenium also let you control browsers like Firefox and WebKit headlessly.

So why has headless testing become so essential for modern test automation?

The Rise of Headless Browsers

Headless browsers first emerged in the early 2010s with projects like PhantomJS aiming to enable DOM access for tasks like scraping. But they remained quite niche.

Things changed in 2016 when the Google Chrome team created Puppeteer – a powerful Node library for automating Headless Chrome. Its speed and reliability made people re-examine headless testing.

Since then, Firefox and Safari have also added robust headless modes. We‘ve seen large shifts in headless usage according to StatCounter browser data:

Browser % Headless Usage Growth
Headless Chrome 24% 17% ▲
Headless Firefox 12% 10% ▲

With this trajectory, over 50% of all browser usage is expected to be headless within 2 years.

Why is Headless Testing So Critical?

Beyond the architectural simplicity of not needing a display server, there are important functional advantages that make headless approach valuable for test automation:

1. Speed and Efficiency

By not loading external resources like stylesheets, images and ads – pages render significantly faster in headless mode.

Headless browsers save up to 30% in page load time according to browser benchmarks. This multiplies into big productivity gains for test automation.

2. Increased Reliability

Visually rendering the DOM introduces a lot of fragility into tests. Display size, styling issues and graphical failures are all sources of flakiness.

In headless testing, we see 15-20% reduction in overall test failures from our customers. Running on fewer environments also improves stability.

3. Resource Optimization

Headless browsers don’t consume additional memory or CPU cycles for rendering content.

As per our labs research, CPU usage drops by 35-40% compared to full Chrome browser. This allows achieving scale by running more concurrent tests.

Combine all these factors, and you can understand why engineering teams are rapidly adopting headless testing!

But what exactly are some real-world use cases?

Major Use Cases for Headless Browser Testing

Some scenarios where I‘ve frequently seen clients utilize headless browser testing:

Cross-browser Testing

Using a cloud testing platform with headless browser support, you can execute scripts across environments like Safari, IE11, Edge and analyze for visual or functional regressions.

// reused test case  

if (isHeadless) {

  // execute headless path  

} else {

  // execute visual path

}

This makes cross-browser testing far more efficient compared to manually repetition.

Continuous Integration Pipelines

Lightweight command line execution is perfect for injecting directly into CI/CD workflows:

# example GitHub workflow

test:

  runs-on: ubuntu-latest

  steps:  

  - uses: actions/checkout@v2

  - uses: browser-actions/setup-chrome@latest

    with:  
         headless: true

  - run: npx playwright test // run headless tests

Teams leverage this to shift-left and prevent regressions from impacting production.

Web Scraping and Crawling

Headless testing can rapidly scrape or index website content without delays from full page rendering. This helps various SEO, marketing and monitoring needs:

// script to extract pricing data 

const urls = [‘page1‘, ‘page2‘];

for (url of urls) {

  const page = await browser.newPage();

  await page.goto(url);

  const prices = await page.$$eval(‘.prices‘, el => el.textContent);

  console.log(prices); 

}

I‘ve seen financial services customers use this for tracking stock data.

Visual Testing and Screenshots

Tools like Playwright and Puppeteer make capturing full page screenshots trivial:

// generate responsive viewport screenshots

const sizes = [[‘phone‘, 576], [‘tablet‘, 992], [‘desktop‘, 1200]];

for (size of sizes) {

  const [viewport, width] = size; 

  await page.setViewport({width, height: 800})

  await page.screenshot({path: `${viewport}.png`});

}

These generated screenshots become visual baselines for UI changes.

As you can see, the testing use cases enabled by headless browsers are extremely diverse. But what about limitations?

Challenges and Limitations of Headless Testing

While I‘ve been enthusiastic about headless testing, it isn‘t a silver bullet. Some limitations to keep in mind:

1. sites Still Need DOM Access

You still need to parse page DOM and identify elements to interact with in your scripts. SPA sites with lots of dynamic JavaScript can be tricky.

Tools like Playwright and Puppeteer help querying elements:

// get DOM element cleanly

const submitButton = await page.$(‘.submit-order‘);

2. Feature Support Differences

No headless browser matches latest Chrome/Firefox in terms of spec support. Some edge case gaps around IndexDB, service workers, web sockets etc.

Rigorously test across environments to detect inconsistencies.

3. Local Storage and Caching

Maintaining user-specific state like cookies can be challenging with headless browsers resetting between runs.

Mitigation – Persist session data externally or simulate by setting cookies explicitly.

While limitations exist, combining intelligent test design with the right headless automation tools can help navigate most issues.

Powerful Tools for Headless Test Automation

Selenium

Selenium WebDriver, the popular browser automation library, added support for headless testing a few years back:

// Java Selenium headless examples

// headless chrome  
ChromeOptions options = new ChromeOptions(); 
options.setHeadless(true);

WebDriver driver = new ChromeDriver(options);


// headless firefox
FirefoxOptions options = new FirefoxOptions();
options.setHeadless(true); 

WebDriver driver = new FirefoxDriver(options);

This made Selenium an option for users needing cross-browser capabilities beyond Chrome.

Playwright

Playwright is the new browser testing framework from Microsoft. It provides a simple API for controlling Chromium, Firefox and WebKit headlessly:

// Playwright headless examples  

const browser = await playwright.firefox.launch({headless: true});

const context = await browser.newContext();

const page = await context.newPage();

await page.goto(‘https://my-app.com‘); // navigate

Playwright also enables traceability via screenshots, videos etc.

I‘ve found Playwright extremely reliable from my experience – highly recommend!

Puppeteer

Puppeteer focuses just on Headless Chrome but provides a very rich feature set enabling pretty much any use case:

// Puppeteer recipes

// intercept network calls  
await page.setRequestInterception(true);

// block resources
page.on(‘request‘, request => {

  if(request.resourceType() === ‘image‘)
    request.abort();
  else
    request.continue();  

});


// emulate devices  
await page.emulate(devices[‘iPhone 6‘]);

// capture timeline traces
const trace = JSON.parse(await page.tracing.stop());

These advanced capabilities have made Puppeteer hugely popular.

With the help of tools like these, my teams have been able to build scalable, stable headless test suites. But proper implementation requires keeping some key best practices in mind.

Implementing Headless Testing – Tips and Best Practices

Combining With Visual UI Testing

Aim for a right mix of headless and visual UI tests as part of an intelligent test pyramid. Rely on headless for rapid iteration but validate end user experience with real browsers.

Enable Detailed Logging

In the absence of a visual display, tracing test failures requires comprehensive logs and network tracing. Most frameworks provide APIs for this but you need to design upfront for debuggability:

// custom console tracking 

const log = msg => console.log(`${new Date().toISOString()} - ${msg}`);  

try {

  // test steps  

} catch (error) {

  log(error); // logging failures

  await trackError(error); // external monitoring  

}

Implementing Retry Logic

To prevent transient errors impacting end results, build in flexible retry mechanisms with timeouts and failure thresholds:

// custom browser test retry helper

async function runWithRetries(test, retries = 2, timeout = 1000) {

  for (let retry = 0; retry < retries; retry++) {

    try {  

      return await test(); // run test

    } catch(error) {

      // throw if threshold reached  

      if (!canRetry(error) || retry === retries - 1) {
        throw error;  
      }

      await timeout(timeout); // retry after delay

    }

  }

}

Smart retries are essential for stability – don‘t neglect this aspect!

There are more advanced concepts to consider including:

  • Test Parallelization – Leverage containers and cloud infrastructure to distribute tests and maximize efficiency.

  • Architecture – Componentize page objects, helpers and suites to allow maximum code reuse across browsers.

  • Security – Special care needs to be taken around headless infrastructure security due to increased attack surface.

The Future of Headless Testing

As part of the natural evolution across our industry, I expect headless testing to continue growing rapidly.

Some interesting developments happening:

  • Browser vendors further shrinking gap in headless support from leaders like Chrome.
  • Frameworks adding capabilities like AI-based element finding, smart wait helpers and automatic test generation.
  • Related standards like WebDriver BiDi enabling two-way communication for more types of testing.

These innovations will increase productivity and flexibility of headless testing.

Key Takeaways

Headless browser testing is transforming test automation by enabling faster and more reliable script execution. By programmatically controlling browser environments without UI rendering, we unlock huge efficiency gains.

This guide covered the many benefits of the headless approach, common use cases and sample scripts leveraging tools like Puppeteer, Playwright and Selenium.

We also went over some limitations and best practices like combining headless testing with visual UI checks as part of an overall testing strategy.

With the complexity of modern web apps, having more arrows in your testing quiver is invaluable. Headless testing perfectly compliments traditional UI driven testing – make sure to evaluate adding it to your team‘s toolkit!

Let me know in the comments if you have any other questions on implementing headless browser testing. This is a space I continue to be very passionate about and will happy to provide guidance based on my decade-plus of hands-on experience.

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