Unit testing WordPress plugin in isolation with WP_Mock

In Unit Testing, the word “Unit” actually denotes testing the code in small chunks, that is small units. So what does it mean? Testing each method in a class without any other dependencies. In the WordPress world, testing code without WordPress dependency? Is it possible? Yup, it is, with the help of WP_Mock.

WP_Mock is an API mocking framework, built and maintained by 10up for the purpose of making it possible to properly unit test within WordPress.

10up

WordPress plugins are a cornerstone of the platform’s extensibility, allowing developers to add custom functionality to their websites. However, with great power comes great responsibility, and it’s essential to ensure that your plugins work reliably and as intended. That’s where unit testing comes into play. In this post, we’ll explore how to perform unit testing on WordPress plugins in isolation using the WP_Mock library. We’ll also provide you with a sample code snippet to help you get started.

Read my previous posts on setting up the PHPUnit for a WordPress plugin.

Why Unit Testing Matters for WordPress Plugins

Unit testing involves testing individual units of code, usually functions or methods, in isolation. This practice helps catch bugs and ensure that your code behaves as expected. For WordPress plugins, unit testing is especially crucial because:

1. Quality Assurance: Unit tests help identify issues early in the development process, reducing the likelihood of releasing buggy code.
2. Refactoring: Unit tests provide a safety net when you need to refactor or modify your code. They ensure that existing functionality remains intact.
3. Collaboration: When working with a team, unit tests make it easier for multiple developers to work on the same codebase without inadvertently breaking each other’s code.

WP_Mock

WP_Mock is a library designed to help you isolate your WordPress plugin code from external dependencies and WordPress core functions. It provides a framework for creating mock objects and expectations, allowing you to simulate the behavior of WordPress functions without actually invoking them. This isolation makes your unit tests more reliable and efficient.

Getting Started with WP_Mock

Let’s dive into a simple example to demonstrate how to use WP_Mock for unit testing a basic WordPress plugin. Suppose we have a function named my_plugin_get_title() that retrieves the post title by post ID:

function my_plugin_get_title($post_id) {
    return get_the_title($post_id);
}

Here’s how you can write a unit test for this function using WP_Mock:

// Include the necessary files for WP_Mock
require_once 'path-to/wp_mock/autoload.php';

// Define the test case
class MyPluginTest extends \WP_Mock\Tools\TestCase {

    public function setUp() {
        // Set up WP_Mock
        \WP_Mock::setUp();
    }

    public function tearDown() {
        // Tear down WP_Mock
        \WP_Mock::tearDown();
    }

    public function test_my_plugin_get_title() {
        // Set up expectations
        \WP_Mock::userFunction('get_the_title')
            ->times(1)
            ->with(42)
            ->andReturn('Sample Post Title');

        // Call the function
        $result = my_plugin_get_title(42);

        // Assertions
        $this->assertEquals('Sample Post Title', $result);
    }
}

In this example, we’re using WP_Mock to mock the get_the_title() function, specifying that it should be called once with the argument 42 and should return 'Sample Post Title'. We then call our my_plugin_get_title() function with the same argument and assert that the result matches our expected title.

Conclusion

Unit testing is an essential practice for developing robust and reliable WordPress plugins. WP_Mock provides a powerful way to isolate your plugin code from external dependencies, making your tests more focused and accurate. By following the principles demonstrated in this post and using libraries like WP_Mock, you can confidently develop and maintain high-quality WordPress plugins.

Remember that this is just a starting point. As your plugin grows in complexity, your unit tests should cover a wider range of scenarios. Happy testing!