The problem

Software Factory is a full-stack software development platform: it hosts repositories, a bug tracker and CI/CD pipelines. It is the engine behind RDO's CI pipeline, but it is also very versatile and suited for all kinds of software projects. Also, I happen to be one of Software Factory's main contributors. :)

Software Factory has many cool features that I won't list here, but among these is a unified web interface that helps navigating through its components. Obviously we want this interface thoroughly tested; ideally within Software Factory's own CI system, which runs on test nodes being provisioned on demand on an OpenStack cloud (If you have read Tristan's previous article, you might already know that Software Factory's nodes are managed and built by Nodepool).

When it comes to testing web GUIs, Selenium is quite ubiquitous because of its many features, among which:

  • it works with most major browsers, on every operating system
  • it has bindings for every major language, making it easy to write GUI tests in your language of choice.¹

¹ Our language of choice, today, will be python.

Due to the very nature of GUI tests, however, it is not easy to fully automate Selenium tests into a CI pipeline:

  • usually these tests are run on dedicated physical machines for each operating system to test, making them choke points and sacrificing resources that could be used somewhere else.
  • a failing test usually means that there is a problem of a graphical nature; if the developer or the QA engineer does not see what happens it is difficult to qualify and solve the problem. Therefore human eyes and validation are still needed to an extent.

Legal issues preventing running Mac OS-based virtual machines on non-Apple hardware aside, it is possible to run Selenium tests on virtual machines without need for a physical display (aka "headless") and also capture what is going on during these tests for later human analysis.

This article will explain how to achieve this on linux-based distributions, more specifically on CentOS.

Running headless (or "Look Ma! No screen!")

The secret here is to install Xvfb (X virtual framebuffer) to emulate a display in memory on our headless machine …

My fellow Software Factory dev team and I have configured Nodepool to provide us with customized images based on CentOS on which to run any kind of jobs. This makes sure that our test nodes are always "fresh", in other words that our test environments are well defined, reproducible at will and not tainted by repeated tests.

The customization occurs through post-install scripts: if you look at our configuration repository, you will find the image we use for our CI tests is sfstack-centos-7 and its customization script is

We added the following commands to this script in order to install the dependencies we need:

sudo yum install -y firefox Xvfb libXfont Xorg jre
sudo mkdir /usr/lib/selenium /var/log/selenium /var/log/Xvfb
sudo wget -O /usr/lib/selenium/selenium-server.jar
sudo pip install selenium```

The dependencies are:

* __Firefox__, the browser on which we will run the GUI tests
* __libXfont__ and __Xorg__ to manage displays
* __Xvfb__
* __JRE__ to run the __selenium server__
* the __python selenium bindings__

Then when the test environment is set up, we start the selenium server and Xvfb
in the background:

/usr/bin/java -jar /usr/lib/selenium/selenium-server.jar -host >/var/log/selenium/selenium.log 2>/var/log/selenium/error.log
Xvfb :99 -ac -screen 0 1920x1080x24 >/var/log/Xvfb/Xvfb.log 2>/var/log/Xvfb/error.log```

Finally, set the display environment variable to :99 (the Xvfb display) and run your tests:

export DISPLAY=:99

The tests will run as if the VM was plugged to a display.

## Taking screenshots

With this headless setup, we can now run GUI tests on virtual machines within our
automated CI; but we need a way to visualize what happens in the GUI if a test

It turns out that the selenium bindings have a screenshot feature that we can use
for that. Here is how to define a decorator in python that will save a screenshot
if a test fails.

import functools
import os
import unittest
from selenium import webdriver


def snapshot_if_failure(func):
    def f(self, *args, **kwargs):
            func(self, *args, **kwargs)
        except Exception as e:
            path = '/tmp/gui/'
            if not os.path.isdir(path):
            screenshot = os.path.join(path, '%s.png' % func.__name__)
            raise e
    return f

class MyGUITests(unittest.TestCase):
    def setUp(self):
        self.driver = webdriver.Firefox()

    def test_login_page(self):

If test_login_page fails, a screenshot of the browser at the time of the exception will be saved under /tmp/gui/test_login_page.png.

Video recording

We can go even further and record a video of the whole testing session, as it turns out that ffmpeg can capture X sessions with the "x11grab" option. This is interesting beyond simply test debugging, as the video can be used to illustrate the use cases that you are testing, for demos or fancy video documentations.

In order to have ffmpeg on your test node, you can either add compilation steps to the node's post-install script or go the easy way and use an external repository:

# install ffmpeg
sudo rpm --import
sudo rpm -Uvh
sudo yum update
sudo yum install -y ffmpeg

To record the Xfvb buffer, you'd simply run

export FFREPORT=file=/tmp/gui/ffmpeg-$(date +%Y%m%s).log && ffmpeg -f x11grab -video_size 1920x1080 -i$DISPLAY -codec:v mpeg4 -r 16 -vtag xvid -q:v 8 /tmp/gui/tests.avi ```

The catch is that ffmpeg expects the user to press __q__ to stop the recording
and save the video (killing the process will corrupt the video). We can use
[tmux]( to save the day; run your GUI tests like so:

export DISPLAY=:99
tmux new-session -d -s guiTestRecording 'export FFREPORT=file=/tmp/gui/ffmpeg-$(date +%Y%m%s).log && ffmpeg -f x11grab -video_size 1920x1080 -i'$DISPLAY' -codec:v mpeg4 -r 16 -vtag xvid -q:v 8 /tmp/gui/tests.avi && sleep 5'
tmux send-keys -t guiTestRecording q

Accessing the artifacts

Nodepool destroys VMs when their job is done in order to free resources (that is, after all, the spirit of the cloud). That means that our pictures and videos will be lost unless they're uploaded to an external storage.

Fortunately Software Factory handles this: predefined publishers can be appended to our jobs definitions; one of which allows to push any artifact to a Swift object store. We can then retrieve our videos and screenshots easily.


With little effort, you can now run your selenium tests on virtual hardware as well to further automate your CI pipeline, while still ensuring human supervision.

Further reading