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Rejoice!

Drupal 8 ships with PHPUnit!

PHPUnit is the PHP industry standard testing framework, and with it comes the potential to make significant gains in the way we test Drupal, both core and contrib.

There’s a lot to be said about setting up, configuring, running and integrating PHPUnit (and how to do it for Drupal in particular), about which there are ample generic resources on the web. http://drupal.org/phpunit is a good starting point; it has crucial links and information, particularly to the PHPUnit manual, which will become your best friend.

So, instead of duplicating what’s already out there, I’m going to focus on some principles that will help you get the most value from PHPUnit on your Drupal 8 sites and contributed modules. Principles go well with a printed medium, anyway – no motive to copy and paste!

Test the Right Thing

It’s important to identify the type of testing you really need to do. PHPUnit is capable of a number of different types: behavioral, functional, and unit, at the least. With Drupal, I tend to use it only for unit and narrowly-scoped functional tests (Simpletest has more tools for conventional Drupal integration testing), and I prefer Behat for behavioral testing.

Regardless of the type of test you’re writing, the first step is to properly understand what you’re testing. In testing parlance, this is the “system under test” (SUT). Clearly identifying the SUT can be surprisingly elusive, especially for those unaccustomed to testing. It is worth taking the time to get it right; a clear, well-understood SUT is the foundation of not only good tests, but good test suites.

When contemplating a unit or functional SUT, I always have one question: “What is the code I’m testing solely responsible for?”