I'm writing tests using phpunit and WP_Mock for a WordPress plugin and I want to return a WP_Error if the method in my class isn't being called correctly (receiving all of the arguments it needs).

The standard way of doing this of course, would be to create and return a new WP_Error at that point - but as WordPress isn't loaded when I run the tests, the WP_Error class doesn't exist.

Other WordPress classes are being mocked and injected with Mockery, but this seems like overkill to test the WP_Error is being thrown; but I'm not seeing any other half-way sensible plan.

Is there a good way to mock the WP_Error?

Easiest way:
Just include_once the file with the definition for WP_Error (wp-includes/class-wp-error.php) when bootstrapping your tests. That way the class will be defined when you need to instantiate the class.

WP_Error doesn't have any other dependencies, so including it should be a big deal.

You are not not testing actual behaviour of the class, but only an object of that class is returned. So no need to mock anything if the proper definition exists.

Better way:
Use WP-CLI to scaffold. Doing that you'd have access to wordpress functions and classes.

You'll need to install WP-CLI and have a working WP installation, with your plugin files in there.

First you'd need to do the plugin scaffolding. In your WP directory run

wp scaffold plugin-tests your-plugin

This will create a set of files in your plugin directory similar to this:

|-bin/

|----install-wp-tests.sh

|-tests/

|----bootstrap.php

|----test-sample.php

|-.travis.yml

|-phpcs.xml.dist

|-phpunit.xml.dist

|-your-plugin.php

You'll need to cd to your plugin directory, and from there run the test environment initialization:

bin/install-wp-tests.sh db_name db_user 'db_password' db_host wp_version

Parameters are self explanatory. wp_version can be latest. On this DB wp-cli will create a set of tables for testing, and it will create a WP installation in your /tmp directory, configured with the above values that will use in each time you run phpunit.

After that, it's a simple matter of calling phpunit and run your tests. You can use the test-sample.phpas a starting point, or copy yours over there.

When running your tests this way, WP_Error will be defined, and you could easily test that your methods are returning it correctly.

Happy testing!

Method 1:

Execute your tests after plugins_loaded action, like:

add_action('plugins_loaded', 'your_func');

function your_func()

{

   ...

}

Method 2:

Include once the WP_error class :

include_once(ABSPATH.'wp-includes/class-wp-error.php');

...

your code

Enable debugging.

define( 'WP_DEBUG', true );

WP_DEBUG is a PHP constant (a permanent global variable) that can be used to trigger the "debug" mode throughout WordPress. It is assumed to be false by default and is usually set to true in the wp-config.php file on development copies of WordPress.

If your debug mode not enabled enable it. Hope you will get all errors info that you need.