Taking Web Testing To The Next Level with Headless Browsers

Hey there!

As technology progresses, web applications are becoming more complex and dynamic. This makes testing them manually an impossible task. Here comes test automation to the rescue!

However, even running hundreds of automated browser tests can get slow and resource intensive.

The solution? Headless browser testing.

If you haven‘t heard of headless testing before, you‘re in for a treat my friend!

In this detailed guide, I‘m going to walk you through:

✅ What headless browser testing is
✅ Benefits and limitations of the approach
✅ Performing headless testing using NightwatchJS – a popular JavaScript automated testing framework
✅ Common issues you might face and how to troubleshoot them

I‘ve been testing complex web apps for over 10 years now on thousands of real desktop and mobile devices. Recently I‘ve been impressed with what headless testing unlocks in terms of speed and stability.

So I‘m excited for you to learn all about it! There‘s a lot to cover, so let‘s get started.

What is Headless Browser Testing?

Let me begin by explaining what a headless browser actually is.

Headless browsers are browsers without a graphical user interface (GUI). They run on a machine the same way Google Chrome or Firefox do, but don‘t render the visual UI.

Under the hood though, they still execute JavaScript, render web pages and can perform everything an ordinary browser can!

Some examples of popular headless browsers are:

• Headless Chrome
• Headless Firefox
• Headless Internet Explorer

So in headless browser testing:

• The tests are run inside headless browsers like Chrome and Firefox
• The browsers access and interact with web pages like normal
• But they don‘t load any visual interface

This allows you to test web apps without needing to see what‘s happening on-screen.

Headless testing is perfect for:

👉 Running large test suites on CI/CD infrastructure
👉 Testing progressive web apps (PWAs)
👉 Checking website accessibility compliance
👉 Doing backend testing without front-end dependencies

And much more! Both manual and automated tests can run via headless browsers.

In this guide, we‘ll specifically see how to use the NightwatchJS automated testing framework to execute headless browser tests.

But first, let me share why headless testing can be a total gamechanger for you.

Benefits of Headless Browser Testing

After running UI tests on thousands of devices for years, let me tell you – headless testing has some unique advantages!

1. Faster Test Execution

Headless tests run 2 to 10x times faster than full browser testing.

Why? Because unlike regular browsers, headless ones don‘t have to load complex front-end UI elements like images, videos, CSS animations, etc.

Tests finish much quicker without all that visual overhead.

For example, a typical JMeter load test by Tricentis showed that headless Chrome was 8x faster at page loading than the regular Chrome browser.

Source: Tricentis

You can run hundreds more test cases in a shorter time with headless execution.

2. Lower Resource Consumption

No UI also means very low memory and CPU load. Browsers hog resources to render all those visual elements.

So headless tests can run on underpowered machines like small Docker containers in CI/CD pipelines.

A test that would overwhelm your system when running visually may just work fine headlessly due to minimal resource usage.

3. Supports Parallel Testing

Together, faster test runs and lower resource usage allows easy parallel test execution.

You can run multiple headless test suites side-by-side without collisions since they don‘t conflict over UI elements.

Doing simultaneous test runs slashes total execution time greatly.

4. Suits Modern Agile Workflows

Headless testing fits right into modern dev workflows like:

• Continuous integration and delivery
• Test automation in containers
• Cross-browser testing
• Developer-driven testing

Its lightweight nature, command line usage and support for languages like JavaScript and Python also appeal to developers and testers alike.

5. Tests Dynamic Pages

Today‘s web apps are highly dynamic – they make heavy use of JS frameworks to render content.

Selenium can sometimes struggle to keep up with dynamic DOM elements.

But headless browsers process JavaScript seamlessly like native browsers. This allows reliable testing of dynamic web pages.

In fact as per Selenium creator Jason Huggins:

“If you are doing to do any kind of JavaScript testing, in 2018, you absolutely should be using a real JavaScript engine.”

Headless browsers provide just that – the latest JavaScript engines for testing modern web applications.

6. Can Execute On Restricted Devices

Special devices like medical equipment, in-vehicle infotainment systems, kiosks have locked down OS permissions.

Testing real user workflows on them requires remote browser control.

Headless mode allows you to test restricted devices easily without installing intrusive binaries. The tests instead run on your machine while controlling the browser remotely.

This makes headless testing a great fit for special use cases like testing embedded systems.

Current Limitations

Of course headless testing isn‘t a silver bullet. There are a few limitations to be aware of:

1. No Visual Feedback

The lack of UI causes a loss of visual feedback during test runs. You can‘t actually see what the tests are doing.

Without screenshots or videos, this makes debugging failures harder. You need to rely on browser console logs, network request tracking, etc.

2. Limited Browser Events Support

Advanced browser interactions like hover, drag and drop, scroll do not fully work in some older headless browsers. Modern ones are improving quickly though.

For example Headless Firefox has very good support for a range of browser events already.

3. Browser Differences Persist

Just because the browsers are running hidden doesn‘t mean browser differences disappear.

For example, Chromium and Gecko use different logic for execution context, DOM handling, CSS selectors and more.

So testing across browsers is still important to catch rendering inconsistencies.

4. Dynamic Content Can Break

While headless browsers do exceptionally well at executing JavaScript, highly dynamic content with unpredictable outcomes can sometimes break tests.

For such complex UI interactions, real visual browser testing is more robust.

5. Limited Ability to Catch Visual Regressions

By definition, visual errors in UI appearance can only be caught by eye.

So headless tests have limited coverage over styling, layout or alignment-related regressions.

Automated visual regression testing on actual browsers can complement headless tests nicely here.

So in summary, headless testing has some deficiencies like no visual feedback, full support for few browser events and inability to catch visual regressions.

But it more than makes up for these limitations through the incredible testing speed, scalability and efficiency it delivers.

Now let‘s look at how to actually implement headless testing using one of my favorite tools – Nightwatch.js.

Introduction to NightwatchJS

Nightwatch.js is an easy-to-use Node.js based end-to-end testing framework for browser-based apps and websites.

It is a complete browser automation solution that uses the powerful W3C WebDriver API to perform commands and assertions on DOM elements.

I love Nightwatch because it has a simple & readable syntax while providing a rich feature set including:

✅ Multi-browser support like Chrome, Firefox and IE
✅ Parallel test execution
✅ Cross-platform compatibility
✅ Page object pattern implementation
✅ Command line test runner
✅ Support for Cucumber BDD
✅ Containers and cloud testing helpers
✅ And so much more!

Nightwatch enjoys 20,000+ weekly downloads on NPM currently and has a strong community following.

Within just a few minutes, you can write automated browser tests with Nightwatch that replicate real user workflows.

And here‘s the best part – Nightwatch has fantastic built-in support for headless testing!

Let‘s look at how that works.

Performing Headless Testing using Nightwatch

The key to enable headless execution in Nightwatch is using the right configuration parameters.

Based on the browser, you need to set some special desiredCapabilities and CLI flags for entering headless mode.

I‘ll walk you through the step-by-step process next.

Running Headless Chrome Testing

Google Chrome is one of the most popular browsers with a mature headless counterpart – Headless Chrome.

Let‘s see how to make tests run on it using Nightwatch.

Step 1: Update Chrome desiredCapabilities in the Configuration File

Open nightwatch.conf.js file and add the following config:

"desiredCapabilities": {

    "browserName": "chrome",

    "goog:chromeOptions": {

      "args": ["headless", "disable-gpu"]

    }

}

This instructs Nightwatch to use Headless Chrome with GPU acceleration turned off.

Step 2: Run Tests as Usual

Now Nightwatch will automatically run all tests in headless mode by default. So just execute tests like before:

npx nightwatch tests/

And you will instantly get headless execution in Chrome! No other changes needed.

Step 3: [Optional] Use CLI Flag

You can also make any test run headless via the command line instead of a config change.

Just add the --headless flag on test execution:

npx nightwatch --headless tests

So either through configs or CLI flags – running Headless Chrome testing via Nightwatch is super easy!

Running Headless Firefox Testing

Similar to Chrome, Firefox also has excellent headless browser support.

Here is how to make Nightwatch do testing on Headless Firefox:

Step 1: Update Firefox desiredCapabilities

Add the following browser config in nightwatch.conf.js:

"desiredCapabilities": {

  "browserName": "firefox",

  "moz:firefoxOptions": {

    "args": ["-headless"]

  }

}

This specifies to use Firefox in headless mode.

Step 2: Run Tests as Usual

Directly executing your test suite will now trigger automated headless testing on Firefox:

npx nightwatch tests

No other code changes needed to shift existing tests to headless mode.

Step 3: [Optional] Use CLI Flag

Similar to Chrome, Firefox headless execution can also be controlled via:

npx nightwatch --headless tests

Pass the --headless flag during test runs to enable it on the fly.

And that‘s really all there is to it! The simple configuration options make it very easy to do headless browser testing with NightwatchJS.

Now let‘s discuss some common pitfalls and how to deal with them effectively.

Troubleshooting Headless Test Failures

While getting started with headless testing is straightforward in Nightwatch, it does come with a unique set of issues.

Here are some common headless testing problems and ways to troubleshoot them:

1. Tests Pass When Run Visually, Fail In Headless Mode

This is a very common scenario – things work fine visibly but break headlessly.

• Turn on verbose debug logs in Nightwatch test runner settings. The logs will show you the exact command when tests fail along with error traces.

• Collect screenshots on test failure using plugins like nightwatch-screenshot so you have some visual context.

• Check for timing issues with dynamic content loading using browser developer tools during headless run.

2. Elements Not Found in Selectors

Stale element reference exceptions or incorrectly declaring selectors can happen frequently.

• Use browser developer tools to test your CSS selectors to ensure they are accurately targeting elements.

• Improve selector quality by using unique IDs, data attributes, container chain patterns.

• Implement waiting for elements to appear before interacting using Nightwatch‘s .waitForElementVisible() API.

3. Intermittent Failures

Tests executing successfully in one run but failing in another run is frustrating.

• Set retry logic using Nightwatch hooks like .beforeEach() to retry failing tests automatically 2-3 times before reporting a failure.

• Use Nightwatch‘s .perform() operation to wrap test logic in a code block to isolate execution context. This shields it from external issues.

• Confirm test order independence by running test cases randomly to uncover coupling between tests.

4. Browser Crashes and Hangs

Headless browsers sometimes freeze up or stop executing suddenly without any error.

• Increase timeouts in desiredCapabilities configs to allow more wait time per step

• Check browser console logs to look for fatal JS errors that crash browser processes

• Monitor memory and CPU with tools like Chrome Task Manager to identify resource overload

The key is proper instrumentation – adding debug logs, screenshots on failure, expanding timeouts etc. to expose what is breaking headlessly.

With the above strategies, you can debug almost any headless testing issue.

Key Takeaways

Let‘s summarize the core things you learned about headless browser testing with NightwatchJS:

✅ Headless testing runs browser tests without UI rendering resulting in faster execution

✅NightwatchJS has built-in configuration support for launching Headless Chrome and Headless Firefox

✅ Switching existing tests to headless mode requires just basic config changes

✅ Faster runs, parallel execution and low resource usage makes headless testing perfect for modern dev workflows

✅ Troubleshoot failures using browser logs, screenshots, test retries and isolation to resolve issues

I hope you now have clarity on leveraging headless testing to advance your test automation approach!

NightwatchJS definitely makes it simple to unlock additional speed and testing coverage with headless browser execution.

I highly recommend giving it a try on your next web application project.

Let me know if you have any other questions!