Sass Unit Testing with True

True is a library to provide unit testing for Sass. Today we are taking a brief look at how it works and how it can be incorporated into a project. While this won’t necessarily be something that you use on every project it is helpful if you are building a framework or set of standardized Sass files that you plan to re-use on other projects.

An Example of Usage

You can see basic usage of True to verify a function is behaving as expected. For purposed of our example I’m simply taking the unpack function from Thoughtbot’s Bourbon. Scroll to the bottom of the SCSS to see the tests and click “View Compiled” button (available on hover) to view the test output.

See the Pen Sass Unit Testing with True by Matt Vanderpol (@bookwyrm) on CodePen.

Thoughts on organizing into a project

As you can see, this can make your generated CSS fairly messy and you need to import the true library and actually look at your generated CSS to see what happens. While this is fine for exploring, we want something cleaner for a project.

With that in mind, True offers a few options which we can leverage.

JavaScript Test Runner

True provides a way to do tests with a JavaScript test runner. See Project Setup below for details on how to get this to work.

This is a good way to handle tests and has a nice, clean output.


Command Line Test Runner

True also provides a CLI for running tests with ruby-sass – but it requires the ruby gem to be installed.

While it might work basic tests, this is not recommended for regular usage. Issues with it include:

  • No output on success – you are left wondering if it even ran
  • Very cluttered output on failure – you definitely know when it failed
  • Requires ruby gem


Project Setup

I have created a sample project in GitHub (testing-sass-with-true) which you can clone to see a working example.

SCSS Organization

The Sass files that are responsible for building CSS for the site are all in the scss/ directory as you would expect.

Test Organization

All test files are contained in the test/ directory and they simply import the necessary Sass files from scss/. This keeps our entire setup cleaner and keeps the test code from polluting the generated CSS.

Running Tests

I have used npm for simplicity here, based on I will explore using Grunt or Gulp in a followup article.

JS Tests

To run the JS tests all you have to do is:

  1. setup npm via npm install
  2. run the tests via npm test

You can see the nice colored output from the test runner.

CLI Tests

To see the CLI tests you need to first install the Ruby gem with bundle install. Then you can see both passing and failing tests:

  • passing tests with: true-cli test/test.scss
  • failing tests with: true-cli test/fail-example.scss

In Conclusion

True is a nice library and provides good support for unit testing your Sass to be sure it is doing what you expect. Just be sure that you setup your project in such a way to support it.