Increasing Build IQ with Travis CI

Continuous Integration is a must these days. And for social, open source projects it’s crucial. Our tool of choice for automated testing is Travis CI. Like most tools, Travis does what it does well. Unfortunately it’s not very “smart”. Heaven help you if you have a large or modular project with a multitude of tests - you’ll be waiting an eternity between builds.

And that’s exactly what we ran into. We have a repository that contains 30 NPM modules, each with their own specs (tests). These modules are part of an aging assets pipeline that I briefly mentioned last week. As such each module is subject to a litany of tasks each time a change is made. Travis CI is hooked into the repo and for each Pull Request would run specs for every module, assuring that there are no errors in the code changes contained in the PR. When you’re only working on one or two modules the run-time for the tasks is relatively low; typically 1 - 2 minutes. That of course depends on things such as npm install time, as each module requires an install for testing. Multiply that by 30 and you start to see where the problem arises.

Waiting Sucks

Without targeted build testing we’re left waiting or task-shifting until the build completes successfully. Our need was clear: figure out what files were affected, map and filter the results, and run only the specs for the modules changed in any particular Pull Request or push. That’s where travis-target comes into play.

Here’s a snippet of our repo structure, for reference:

ui-tracking
|--src
   |--common
      |--event_registry
      |--tracking_metadata
   |--tracking
      |--cart
      |--etc..

Target Acquired

In order to target modules, we need to know what their normalized names are; the names that we publish them to NPM under. Because of some legacy stuff baked into our pipeline, we store modules at group/name but publish them as group.name. So let’s fire up travis-target (bear in mind we’re using ES6 syntax that Node v7 supports).

const target = require('travis-target');
const pattern = /^src\//;

let targets = await target();

Let’s pretend that the common.event_registry and tracking.cart modules were both modified in one Pull Request (a common pattern for us) - our results would could look like this:

[
  'README.md',
  'src/common/event_registry/js/event_registry.js',
  'src/common/event_registry/js/registry.js',
  'src/common/event_registry/package.json',
  'src/tracking/cart/js/cart.js',
  'src/tracking/cart/package.json'
]

But that’s just silly, so let’s give travis-target some options to work with:

const target = require('travis-target');
const pattern = /^src\//;

let targets = await target({
  pattern: pattern,
  map: (result) => {
    let parts;

    result = result.replace(pattern, '');
    parts = result.split('/');

    return parts.slice(0, 2).join('.');
  }
});

By passing pattern in options, we’re telling travis-target to filter on (or return only those results which match) the regular expression pattern. That gives us an initial result set of directories starting with src/.

[
  'src/common/event_registry/js',
  'src/tracking/cart/js'
]

You’ll notice that the initial example of results contained some duplicate directories; travis-target cleans that up for you.

Next, we specify the map function on options. That’ll let us transform the each element in the Array of results so that it’s ready to use. Our results would now look like this:

[
  'common.event_registry',
  'tracking.cart'
]

Great Justice

Using this last result set, we now know which modules were affected in the PR, and we know which modules to run specs for. Our next steps are firing off a sequence of shell commands using @exponent/spawn-async, which plays nicely with async/await patterns now supported in Node v7.1 with the --harmony-async-await flag.

Since we implemented this pattern, build times for our PRs are in the 1-2 minute range; a vast improvement and one sure to bring developer happiness in some small degree.

Cheers!