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(Not really) headless browser test execution.

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28 / Apr  2019

Do you participate in a project which has automated UI tests? Do you get annoyed by the fact that your CI environment is flaky because of UI tests? Do you have enough of maintaining multiple slave nodes of your Jenkins installation just for the sake of OS specific browser behaviour? If you find any of the questions familiar, please read this article where I try to explain what drove me to an obvious solution for a configuration madness I was going through in every project.

How do you run your UI based tests?

Many, many times in previous projects I was questioning myself, why we keep a VM (or couple of them) together with a Firefox/Chrome installation just for the sake of runnning UI tests. Discussions with QA never really resulted in any different approach. Until a point, sometime in 2017, when I was helping another team with migrating from Jenkins to GitlabCI. They had their own test automation framework (also UI based) which in previous configuration was using a jenkins-slave-node with Chrome or Firefox inside it, running inside a X session. The team wanted to move to GitlabCI for their CI pipelines, but they didn’t know how to tackle the UI based tests.

The approach I’m describing is nor new nor really innovative. I was even surprised myself that I haven’t thought of it years before.

xvfb to the rescue

After quick research, I’ve found a solution to use headless option to run UI tests. Unfortunately, the team was bound to a Firefox version which did not have a headless option yet. Turned out that another approach was to use xvfb. If I recall correctly I was following this blog article in order to get the tests running. With xvfb at disposal, the UI testing job could still run a browser within a X session, but without the need to actually display it. Furthermore, I already understood that I can containerize xvfb to leverage the gitlab runner docker executor, which spawns docker containers for every executed job. Well, that’s great sounds like job done.

Applied solution

Unfortunately, I don’t have the source code I created two years ago, to show the real solution. That’s why I decided (for the sake of completeness of this post) to fork the Selenide project (which has UI tests inside) and show how one could run ‘headless’ tests as I configured them. But before showing the code, let me repeat that the automated framework was bound to Firefox version 63.0.3. For this version the real headless option was not available yet - which forced me to create the image in the first place. Additionally, to show how to use headless browsers I’ve added those options to the project as well.


  - test

.job_template: &test_job
    - master
  stage: test
    LANG: C.UTF-8
    LC_ALL: C.UTF-8

'Firefox xvfb':
  <<: *test_job
    - xvfb-run -a ./gradlew firefox

'Firefox Headless':
  <<: *test_job
    - ./gradlew firefox_headless

'Chrome Headless':
  <<: *test_job
    - ./gradlew chrome_headless

In this snippet I’ve run the tests in three different base images, with different options:

For the presentation purposes I needed to build the standalone-firefox:latest and standalone-chrome:latest images myself, as Selenide uses Gradle as a tests runner, which in turn needed at least a JDK available. The presented image description can be found at

The xvfb-firefox:latest is an image with xvfb and Firefox in the specified version. To make firefox in this version work, I needed to install aditional libraries and the gecko driver.

What’s visible inside the .gitlab-ci.yml file is that there’s a stage in which 3 sets of tests are being executed, each with a different option:

That can also be seen in the pipeline You can see that the Firefox and Chrome Headless tests are failing. I did not focus on them too much, as the failures appear only for 2 of 474 tests. For the sake of this post I did not investigate. Coming back to the xvfb based approach, by wrapping our command into xvfb-run -a <command> we actually run an in memory X display, which then in turn has firefox opened. Quite interesting, right? :) Hence, our tests can run inside a container.

As a side note, any artifacts by the tests (like a screenshot with a failure) could be stored inside Gitlab using the Job Artifacts feature. Though I haven’t shown that in my example it is pretty straight forward to use. Same for the test reports.

Alternative approaches

I’ve tackled the problem in the aforementioned way. But was it the best one? For the time being I thought so. However, I’d like to point out, that there are other ways to solve the same problem.

Headless browsers

Starting from 59 version of Chrome, it offers a headless functionality, which does not require any X session to be available. It runs purely inside memory - that’s a nice alternative to xvfb solution. In my case, as stated previously, the tests were bound to a specific version of a browser, which didn’t have headless option yet. I didn’t really try to adjust the tests to run in newer browser - I estimated that this would be more time-consuming approach.

Selenium Images and Dockerized Selenium Grid

Instead of building own image whith the browser that’s needed, one could go for an already predefined image from Selenium as I’ve shown for the not-xvfb options.

Maintaining Selenium Grid would eventually end up in lots of work around the hub and the nodes, so there’s an easier solution to that. Just dockerize Selenium Grid and enjoy the possibility of having it configured and deployed anywhere you like. In this article the author shows how to setup dockerized Selenium Grid with minimal effort. What’s more, one could use Docker Swarm or Kubernetes as the orchestration platform for Selenium Grid. One thing I haven’t really thought through as it comes to this approach is multi OS configuration - on one hand, I think that shouldn’t be impossible knowning all the tools. On the other hand, I think that a xvfb-based-headless approach for older browsers might be impossible to achieve on a Windows container.

Cloud solutions

If you are lucky enough to have the freedom to choose cloud-based solutions in your company (believe me that some companies still restrain from it in 2019), there are some options for you, like:

Those are just couple of solutions I found on the internet. I haven’t tested any of them, but they’re there if you need them. All of the solutions are claiming to have Selenium Grid underneath, and what would be interesting for me is whether I really need to base my UI tests on Selenium, to actually leverage them?


What have I learnt in general about approaches to UI tests, besides the obvious technical possibilities? I think that questioning the status quo is something really needed in the projects we’re building. It happens many times that we, in IT projects, tend to follow the principles and solutions which were chosen years ago. The technology, solutions and approaches evolve almost constantly. Not saying we should follow them blindly, but at least keep track on what’s going on, and choose what’s appropriate for the project we’re working on. Under the circumstances of normal development, this is quite a big effort which needs to be taken.