WordPress Plugin Testing

Model note: Bootstrap and CI config setup are mechanical (haiku). Writing meaningful test cases (choosing fixtures, mocking the right layer, testing edge cases) requires understanding the plugin's code — use sonnet. Redirect/exit harness setup is a one-time pattern and works on haiku.

Set up and write automated tests for WordPress plugins: PHPUnit integration tests (real WP + DB), pure unit tests (no WP loaded), and acceptance/E2E tests with Codeception.

When to use

• "Set up PHPUnit tests for my plugin", "bootstrap a WP test suite", "scaffold plugin tests".
• "Write a unit test for this function", "mock WordPress functions without loading WP".
• "Set up Codeception / wp-browser", "write acceptance tests".
• "Test a hook callback", "assert a filter changes the output", "test AJAX handlers".
• "Add tests to CI", "run tests on GitHub Actions".

Not for: PHPStan static analysis — use the official wp-phpstan skill. Scaffolding a stubs package for a third-party library — use wp-phpstan-stubs. Debugging CI failures on an existing suite — use wp-ci-qa.

Method

1. Choose test type

Start with integration tests for hooks/filters; unit tests for pure business logic; acceptance only for critical user flows.

2. Integration test setup (WP test suite)

Install test suite:

# WP-CLI method (recommended)
wp scaffold plugin-tests my-plugin

# Manual — install WP test library
bash bin/install-wp-tests.sh wordpress_test root '' localhost latest

bin/install-wp-tests.sh creates a temp WP installation and the wordpress-tests-lib. Add tests/ dir to .gitignore if downloading WP inline, or commit the bootstrap only.

`composer.json` additions:

{
    "require-dev": {
        "phpunit/phpunit": "^9.0 || ^10.0",
        "yoast/phpunit-polyfills": "^2.0"
    },
    "scripts": {
        "test": "phpunit",
        "test:unit": "phpunit --testsuite=unit",
        "test:integration": "phpunit --testsuite=integration"
    }
}

`phpunit.xml.dist`:

<?xml version="1.0"?>
<phpunit bootstrap="tests/bootstrap.php" colors="true">
    <testsuites>
        <testsuite name="integration">
            <directory>tests/integration</directory>
        </testsuite>
        <testsuite name="unit">
            <directory>tests/unit</directory>
        </testsuite>
    </testsuites>
</phpunit>

`tests/bootstrap.php` (integration):

<?php
$_tests_dir = getenv( 'WP_TESTS_DIR' ) ?: '/tmp/wordpress-tests-lib';
require_once $_tests_dir . '/includes/functions.php';

tests_add_filter( 'muplugins_loaded', function() {
    require dirname( __DIR__ ) . '/my-plugin.php';
} );

require $_tests_dir . '/includes/bootstrap.php';

3. Write integration tests

Extend WP_UnitTestCase (provided by WP test suite). It wraps each test in a DB transaction and rolls back — no teardown needed for posts/users/terms.

class Test_My_Feature extends WP_UnitTestCase {

    public function test_filter_changes_title() {
        $post_id = self::factory()->post->create( [ 'post_title' => 'Original' ] );

        // Activate the plugin feature
        add_filter( 'the_title', 'my_plugin_modify_title', 10, 2 );

        $title = get_the_title( $post_id );

        $this->assertStringContainsString( 'Modified', $title );
    }

    public function test_option_saved_on_activation() {
        do_action( 'activate_my-plugin/my-plugin.php' );

        $this->assertSame( '1.0.0', get_option( 'my_plugin_version' ) );
    }

    public function test_ajax_handler_returns_json() {
        // Simulate AJAX call
        $_POST['_wpnonce'] = wp_create_nonce( 'my_action' );
        $_POST['data']     = 'test';

        try {
            $this->_handleAjax( 'my_plugin_action' );
        } catch ( WPAjaxDieContinueException $e ) {
            // Normal for wp_send_json_success
        }

        $response = json_decode( $this->_last_response, true );
        $this->assertTrue( $response['success'] );
    }
}

Factory helpers:

$user_id    = self::factory()->user->create( [ 'role' => 'editor' ] );
$term_id    = self::factory()->term->create( [ 'taxonomy' => 'category', 'name' => 'News' ] );
$post_ids   = self::factory()->post->create_many( 5, [ 'post_status' => 'publish' ] );
$attachment = self::factory()->attachment->create_upload_object( '/path/to/image.jpg' );

4. Unit tests with Brain\Monkey (or WP_Mock)

For pure functions that don't need a real WP environment. Brain\Monkey is the recommended choice — it includes Mockery, has first-class stubEscapeFunctions() / stubTranslationFunctions() helpers, and richer hook assertion API. WP_Mock (10up) is a lighter alternative.

# Brain\Monkey (recommended)
composer require --dev brain/monkey mockery/mockery yoast/phpunit-polyfills

# WP_Mock (alternative)
composer require --dev 10up/wp_mock

See references/brain-monkey-patterns.md for the full base-class pattern (including ReflectsObjects for testing private/protected members) that matches real-world complex plugin structures.

`tests/bootstrap-unit.php`:

<?php
WP_Mock::bootstrap();
require dirname( __DIR__ ) . '/includes/functions.php'; // file under test

Test:

use WP_Mock\Tools\TestCase;

class Test_Pure_Function extends TestCase {

    public function setUp(): void {
        parent::setUp();
        WP_Mock::setUp();
    }

    public function tearDown(): void {
        WP_Mock::tearDown();
        parent::tearDown();
    }

    public function test_get_plugin_option_returns_default() {
        WP_Mock::userFunction( 'get_option' )
            ->with( 'my_plugin_setting', 'default_value' )
            ->andReturn( 'default_value' );

        $result = my_plugin_get_setting();

        $this->assertSame( 'default_value', $result );
        WP_Mock::assertActionsCalled();
    }

    public function test_action_fires_on_save() {
        WP_Mock::expectAction( 'my_plugin_after_save', 42 );
        WP_Mock::userFunction( 'update_option' )->andReturn( true );

        my_plugin_save_data( 42 );
    }
}

5. HTTP request mocking

Intercept wp_remote_get/post in integration tests:

// In setUp or individual test
add_filter( 'pre_http_request', function( $preempt, $args, $url ) {
    if ( str_contains( $url, 'api.example.com' ) ) {
        return [
            'response' => [ 'code' => 200, 'message' => 'OK' ],
            'body'     => wp_json_encode( [ 'status' => 'ok', 'data' => [] ] ),
            'headers'  => [],
            'cookies'  => [],
        ];
    }
    return $preempt;
}, 10, 3 );

6. Multisite tests

class Test_Network_Feature extends WP_UnitTestCase {

    public static function setUpBeforeClass(): void {
        parent::setUpBeforeClass();
        if ( ! is_multisite() ) {
            self::markTestSkipped( 'Multisite required.' );
        }
    }

    public function test_option_per_site() {
        $site_id = self::factory()->blog->create();

        switch_to_blog( $site_id );
        update_option( 'my_plugin_setting', 'site-value' );
        restore_current_blog();

        switch_to_blog( $site_id );
        $value = get_option( 'my_plugin_setting' );
        restore_current_blog();

        $this->assertSame( 'site-value', $value );
    }
}

Run multisite tests: WP_MULTISITE=1 vendor/bin/phpunit

7. Testing redirect + exit paths

Production code commonly ends with:

wp_safe_redirect( $url );
exit;

add_filter( 'wp_redirect', '__return_false' ) stops the header but not exit — the PHP process dies, PHPUnit prints no summary, and all subsequent tests never run.

Fix: throw from the filter to unwind the stack before `exit` is reached.

// tests/Support/Redirect.php — own PSR-4 file so every test class can catch it
namespace MyPlugin\Test;
class Redirect extends \Exception {
    public string $location;
    public function __construct( string $location ) {
        parent::__construct( 'redirect' );
        $this->location = $location;
    }
}

class Test_With_Redirect extends WP_UnitTestCase {

    private $redirect_filter;

    public function setUp(): void {
        parent::setUp();
        // Whitelist external hosts exactly as production does
        add_filter( 'allowed_redirect_hosts', fn( $h ) => array_merge( $h, [ 'dashboard.example.com' ] ) );
        $this->redirect_filter = static fn( $loc ) => throw new \MyPlugin\Test\Redirect( $loc );
        add_filter( 'wp_redirect', $this->redirect_filter );
    }

    public function tearDown(): void {
        remove_filter( 'wp_redirect', $this->redirect_filter );
        parent::tearDown();
    }

    private function run(): ?string {
        try {
            my_plugin_do_thing_that_may_redirect();
        } catch ( \MyPlugin\Test\Redirect $e ) {
            return $e->location;
        }
        return null;
    }

    public function test_redirects_on_success(): void {
        $location = $this->run();
        $this->assertSame( 'https://dashboard.example.com/', $location );
        $this->assertSame( $user_id, get_current_user_id() ); // side effects before exit
    }

    public function test_no_redirect_on_error(): void {
        $this->assertNull( $this->run() );
    }
}

Copy-paste harness: references/example-test.php. AJAX / REST / wp_die() patterns: references/redirect-assertions.md.

8. GitHub Actions CI

# .github/workflows/phpunit.yml
name: PHPUnit

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    services:
      mysql:
        image: mysql:8.0
        env:
          MYSQL_ROOT_PASSWORD: root
          MYSQL_DATABASE: wordpress_test
        options: --health-cmd="mysqladmin ping" --health-interval=10s

    steps:
      - uses: actions/checkout@v4
      - uses: shivammathur/setup-php@v2
        with:
          php-version: '8.1'
          extensions: mysqli
          tools: composer, wp-cli

      - run: composer install --no-interaction --prefer-dist

      - name: Install WP test suite
        run: bash bin/install-wp-tests.sh wordpress_test root root 127.0.0.1 latest

      - run: vendor/bin/phpunit --testsuite=integration
      - run: vendor/bin/phpunit --testsuite=unit

Common Mistakes

Notes

• WP_UnitTestCase rolls back DB after each test — use self::factory(), not raw wp_insert_post(), so rollback is tracked.
• Integration tests require a real MySQL database; they're slow in CI. Separate unit and integration into distinct test suites and run unit suite on every push, integration suite on PRs only.
• For WooCommerce plugin tests, include WC's test helpers: require WC_ABSPATH . 'tests/legacy/includes/wc-helper-product.php'.
• Codeception + wp-browser is the recommended path for acceptance tests; see https://wpbrowser.wptestkit.dev for full docs.
• references/redirect-assertions.md covers AJAX (WP_Ajax_UnitTestCase), REST, and wp_die() assertion patterns. references/phpunit-bootstrap.md has the full bootstrap + CI setup.

References

• references/brain-monkey-patterns.md — Brain\Monkey unit testing patterns: when(), expect(), Mockery integration, and WP function stubs without loading WordPress
• references/example-test.php — Complete copy-paste-ready test harness for code that uses wp_redirect(), wp_die(), and WP AJAX — includes bootstrap and assertion setup
• references/factory-methods.md — WP_UnitTest_Factory methods: post, user, term, comment, attachment, and network sub-factories with rollback behaviour
• references/phpunit-bootstrap.md — Full PHPUnit bootstrap setup: install-wp-tests.sh, suite configuration, CI matrix, and test runner commands
• references/redirect-assertions.md — Redirect assertion patterns: WP_Ajax_UnitTestCase, REST response assertions, wp_die() capture, and status-code testing
• references/test-patterns.md — WordPress plugin test patterns: hook/filter tests, option tests, shortcode tests, and cron scheduling assertions
• references/wp-mock-patterns.md — WP_Mock unit testing patterns: mock setup, teardown, function expectations, filter/action mocking, and test isolation