When do WordPress Unit Tests Run (At Which Hook?)

Writing unit tests for a WordPress plugin recently had me wondering:

When do WordPress unit tests run?

Meaning, at what point during the WordPress lifecycle are unit tests executed?

I ran some checks and determined that most of the action hooks that run during a typical WordPress page load are also run during unit testing, up to and including the posts_selection hook. The wp hook that comes after that is never reached.

List of Action Hooks that Run

Here is a full breakdown of which action hooks run when PHPUnit unit tests are executed. This list of hooks comes from WP’s Action Reference page.

The hooks shown with a strikethrough are never run, and those without a strikethrough are run.

muplugins_loaded
registered_taxonomy
registered_post_type
plugins_loaded
sanitize_comment_cookies
setup_theme
load_textdomain
after_setup_theme
auth_cookie_malformed
auth_cookie_valid
set_current_user
init
widgets_init
register_sidebar
wp_register_sidebar_widget
wp_default_scripts
wp_default_styles
admin_bar_init
add_admin_bar_menus
wp_loaded
parse_request
send_headers
parse_query
pre_get_posts
posts_selection
wp
…and no hooks fire after this point.

So with that knowledge, you can expect that:

• Code that is hooked to plugins_loaded/init/etc. will be reflected in your unit tests.
• Code hooked to a hook that is crossed out in the list above or something after posts_selection will not be reflected in your unit tests.

What About the Rest?

Unit Tests are meant to be used to test individual units (classes/methods/functions) of your code in isolation. In order to test functionality during the rest of the WordPress lifecycle, you can take a look at setting up end-to-end tests using Codeception.

How Did I Determine This?

A few people have asked about how I determined which hooks fire during unit tests. My method for doing so was pretty simple. I threw some constant definitions like this into the main file of a plugin I was unit testing:

add_action( 'plugins_loaded', function() {
    define( 'PLUGINS_LOADED_RAN', true );
} );

…then threw some corresponding checks like this into one of my unit test methods:

echo defined('PLUGINS_LOADED_RAN') ? 'plugins_loaded ran' : 'plugins_loaded did NOT run';

Then depending on which of those messages printed to the command line when I ran phpunit, I was able to tell whether or not each hook had been run. Give it a try if you like and please let me know if any updates to the list above need to be made. Thanks!

Written by Kellen Mace, who lives in Rochester Hills, MI and builds cool stuff on the web. About Kellen // Follow him on Twitter →