CSS Unit Testing

CSS is often not treated as code, but I’d like to make the argument that it should be treated as code. For instance, it needs to be easier to refactor CSS documents, and it needs to be possible to detect when there are CSS rules that are no longer needed.

I’ve read some recent discussions where the question of CSS unit testing has been raised. Many of these discussions devolved into a debate about whether or not CSS was “code”. A lot of these commentators complained about CSS not being a Turing complete language. I’d like to claim that this debate, with respect to unit testing, is a giant waste of time. Whether or not CSS is Turing complete has nothing to do with the reasons why one would like to write tests against CSS.

But to avoid that debate, I’ll avoid describing CSS as code. Instead I’d to propose that CSS is actually a domain specific language that is used to control the the way a browser works. For simplicity, let’s think of CSS as a configuration syntax.

CSS is a language that affects the way that HTML documents are displayed by web browsers. As the use of CSS has increased as the primary method for altering the way information is displayed, HTML documents have become more and more semantic. The additional tags that have been added to HTML 5 have made the documents even more semantic.

This means that HTML is basically just data that is displayed by a web browser. Web browsers have a default way of presenting this information. CSS is used to alter this default presentation, which means that CSS is simply a method for configuring the workings of a browser. Since CSS has an effect on the execution of a program, the web browser in this case, that is used for displaying information, it is important to ensure that the configuration is accurate for the task at hand.

This is where testing comes in. Testing should be employed any time that we want to ensure the correct operation of an application.

So can we stop the bitching and get started on a decent method for testing CSS already? I’ve got some ideas, but I’ll have to write about them later, once I’ve had a chance to work up some experiments.


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