# Testing on Headless CI Systems (Travis CI, Jenkins)

Being based on Chromium, Electron requires a display driver to function.
If Chromium can't find a display driver, Electron will fail to launch -
and therefore not executing any of your tests, regardless of how you are running
them. Testing Electron-based apps on Travis, Circle, Jenkins or similar Systems
requires therefore a little bit of configuration. In essence, we need to use
a virtual display driver.

## Configuring the Virtual Display Server

First, install [Xvfb](https://en.wikipedia.org/wiki/Xvfb).
It's a virtual framebuffer, implementing the X11 display server protocol -
it performs all graphical operations in memory without showing any screen output,
which is exactly what we need.

Then, create a virtual Xvfb screen and export an environment variable
called DISPLAY that points to it. Chromium in Electron will automatically look
for `$DISPLAY`, so no further configuration of your app is required.
This step can be automated with Paul Betts's
[xvfb-maybe](https://github.com/paulcbetts/xvfb-maybe): Prepend your test
commands with `xvfb-maybe` and the little tool will automatically configure
Xvfb, if required by the current system. On Windows or macOS, it will
do nothing.

```sh
## On Windows or macOS, this invokes electron-mocha
## On Linux, if we are in a headless environment, this will be equivalent
## to xvfb-run electron-mocha ./test/*.js
xvfb-maybe electron-mocha ./test/*.js
```

### Travis CI

On Travis, your `.travis.yml` should look roughly like this:

```yml
addons:
  apt:
    packages:
      - xvfb

install:
  - export DISPLAY=':99.0'
  - Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 &
```

### Jenkins

For Jenkins, a [Xvfb plugin is available](https://wiki.jenkins-ci.org/display/JENKINS/Xvfb+Plugin).

### Circle CI

Circle CI is awesome and has Xvfb and `$DISPLAY`
[already set up, so no further configuration is required](https://circleci.com/docs/environment#browsers).

### AppVeyor

AppVeyor runs on Windows, supporting Selenium, Chromium, Electron and similar
tools out of the box - no configuration is required.