Background:

Unit testing is the automated testing of units of source code against assumptions. The goal of unit testing is to write test cases with assumptions that test if a unit of code is truly working as intended. If an assumption fails, a potential issue is exposed, and code needs to be revised.

By definition unit tests do not have dependencies on outside systems; in other words only your code (a single unit of code) is being tested. Integration testing works similarly to unit tests but assumptions are tested against systems of code, moving parts, or an entire application. The phrases unit testing and integration testing are often misused to reference one another especially in the context of WordPress. This article will try to stay consistent with WordPress terminology whether correct or not. Personally, in writing tests for my WordPress plugins/themes I write integration tests which I feel are more useful for a number of reasons that are outside of the realm of this article.

PHPUnit is the defacto library used to run unit and integration tests in PHP and thus server-side WordPress. This article assumes you are familiar with basic concepts of unit testing with PHPUnit.

What is WP_UnitTestCase?

WP_UnitTestCase is a PHP class included in the WordPress core development repository. Using SVN, you can check out that repo like so:

svn co http://develop.svn.wordpress.org/trunk/ wordpress-develop

The WordPress core development repository contains the core WordPress unit tests. Cool, huh? You can setup these tests, run them, and even write your own! Let’s poke around a few WordPress core test files. Open up wordpress-develop/tests/phpunit/tests/actions.php.

Normally, PHPUnit tests are structured like so:

class MyTestSuite extends PHPUnit_Framework_TestCase {
  public function setUp() {
    // This code will run before each test!
  }

  public function tearDown() {
    // This code will run after each test
  }

  public function testBasic() {
    $this->assertTrue( true );
  }
}

However, when writing integration tests for WordPress based applications, there exists a cool API we can leverage: WP_UnitTestCase. Remember how I asked you to open the actions.php file? You will see the test class in there extends WP_UnitTestCase. WP_UnitTestCase provides shortcuts for doing a number of tasks when creating your test cases. The first thing you will need to do to use this API is to require the file in your PHPUnit bootstrap file:

require_once( $tests_dir . '/includes/bootstrap.php' );

Of course you will need to setup $tests_dir appropriately. Within the WordPress core development repository, this bootstrap file lives at /tests/phpunit/includes/bootstrap.php. Including this bootstrap file will “bootstrap setup” WordPress, setup some things for unit testing, and include a number of useful things one of which is WP_UnitTestCase. There are other ways you could include WP_UnitTestCase, but this is by far the easiest.

Let’s setup our test class to use WP_UnitTestCase:

class MyTestSuite extends WP_UnitTestCase {
  public function setUp() {
    parent::setUp();
    // This code will run before each test!
  }

  public function tearDown() {
    parent::tearDown();
    // This code will run after each test
  }

  public function testBasic() {
    $this->assertTrue( true );
  }
}

Notice our class is extending WP_UnitTestCase instead of PHPUnit_Framework_TestCase. You can probably guess that WP_UnitTestCase extends PHPUnit_Framework_TestCase so we can use everything in PHPUnit_Framework_TestCase by extending WP_UnitTestCase plus a bunch more. Also notice within setUp() and tearDown() we are calling the same methods in the parent class; this is extremely important to ensure WP_UnitTestCase is working correctly. WP_UnitTestCase::setUp() and  WP_UnitTestCase::tearDown() do a bunch of magic such as cache clean up and global resets.

WP_UnitTestCase has an instance variable named $factory. Before each of your tests is run $factory is set to a newly instantiated object of type WP_UnitTest_Factory. The meat of WP_UnitTestCase is in this $factory variable. Let’s look some cools way that we can use WP_UnitTestCase.

Creating Blogs within a Network

public function testBasic() {
  $blog_id = $this->factory->blog->create();
  $blog_id_array = $this->factory->blog->create_many( 4 );
}

This is extremely useful for writing test cases that make cross-site assumptions. As you can tell $this->factory->blog->create() creates a blog and returns the new blog ID. $this->factory->blog->create_many( 4 ), creates 4 new blogs and returns an array of the ID’s in order.

If multisite is not setup, this factory will not exist! You can ensure WordPress is bootstrapped as multisite by setting the following constant up in your phpunit.xml file:

<const name="WP_TESTS_MULTISITE" value="1" />

Creating Test Posts

public function testBasic() {
  $post_id = $this->factory->post->create();
  $post_id_array = $this->factory->post->create_many( 4 );
}

Many times when I am writing tests I need to bulk create posts. WP_UnitTestCase let’s you accomplish this very easily. You can pass an array of post args (same as wp_insert_post) like so: create( $args ) and create_many( $num, $args ). If no arguments are passed, generic post_title/post_content info is generated. Post args passed to create_many will be applied to every post created.

Creating Test Comments

public function testBasic() {
  $comment_id = $this->factory->comment->create();
  $comment_id_array = $this->factory->comment->create_many( 4 );
}

Again, we can leverage WP_UnitTestCase to bulk create comments. You can see the ways to use the class is very consistent :). Comment args (like wp_insert_comment) can be passed to create() and create_many() in the exact same way as the post factory.

Creating Test Users

public function testBasic() {
  $user_id = $this->factory->user->create( array( 'user_login' => 'test', 'role' => 'administrator' ) );
  $user_id_array = $this->factory->user->create_many( 4 );
}

WP_UnitTestCase allows us to bulk create users as well. User args (same as wp_insert_user) can be passed to create() and create_many() in the same fashion as the post factory.

Creating Test Terms

public function testBasic() {
  $term_id = $this->factory->term->create( array( 'name' => 'Term Name', 'taxonomy' => 'category', 'slug' => 'term-slug' ) );
  $term_id_array = $this->factory->term->create_many( 4, array( 'taxonomy' => 'category' );
}

Creating bulk terms is slightly different from other factories. Create() and create_many() do take arguments the same was as wp_insert_term(). However, we provide ‘taxonomy’ and ‘name’ as a part of the array rather than as separate parameters.

Conclusion

WP_UnitTestCase contains additional factories for categories, tags, networks, and attachments. They work in a similar fashion as the factories above, so I will let you explore these API’s yourself :). WordPress contains a bunch of other useful API’s for building your test suites such as a system for mocking actions and a test case class for AJAX hooks. I plan on outlining those tools and a few others in future blog posts.