You test your frontend code, right? And you've got a continuous integration system running, right? Right?

Well you should.

Code review is a lot easier when you have a magical system to say All Is Well. At least in principle. There are limits to testing, but that's a whole different bag of worms.

Today I want to share a little nugget that took hours of interneting to find. Thanks to everyone in this and other Stack Overflow threads for originally figuring it out.

The moving parts

First you will need karma-runner. It is the single best JavaScript test runner I have ever used.

Runs in the background when you're working, re-runs tests on file change, and doesn't care whether you're using Jasmine, Mocha, or something else.

And it's so very very fast.

Next you will need Travis.

Any continuous integration service will do really - I've had great success with Circle CI. But this post is about Travis in particular.

You want something that replicates your environment on a server, runs the tests every time you push to a branch, and shows you the result where it matters most. In the pull request.

The problem

When you're working Karma runs in the terminal. That's where you see the output. But the tests themselves run in a browser or two.

You point a browser at http://localhost:9678 and Karma handles the rest.

All fine and good. But you can't do that on Travis. Not directly at least.

People usually resort to PhantomJS. A headless browser that's happy without a GUI. But sometimes your JavaScript doesn't run well in PhantomJS.

I'm currently using CanJS, for instance. It uses a thing that doesn't work in current versions of PhantomJS. It's going to work in the future when PhantomJS catches up. But it doesn't yet.

Chrome is the only option.

The solution

Luckily, Travis boxes come with Chrome pre-installed. We just have to tweak our configuration to use it.

First we have to use .travis.yml to convince the shell we've got a screen after all.

before_install:
  - export CHROME_BIN=chromium-browser
  - export DISPLAY=:99.0
  - sh -e /etc/init.d/xvfb start

We did three things:

• set CHROME_BIN as chromium-browser, because that's what's installed
• set up a fake DISPLAY
• ran xvfb, which is a sort of GUI environment faker thingy. I'm not certain how it works, but it always shows up in these kinds of things.

Then we uuse karma.conf.js to let Karma know, we need a special browser for Travis.

var configuration = {
  // other things

  customLaunchers: {
    Chrome_travis_ci: {
      base: "Chrome",
      flags: ["--no-sandbox"],
    },
  },
};

if (process.env.TRAVIS) {
  configuration.browsers = ["Chrome_travis_ci"];
}

config.set(configuration);

We created a custom browser launcher that runs Chrome with the --no-sandbox option. And we only use it if the tests are running in Travis.

Simple.

Our tests run both locally and on Travis. Rejoice!