MailCancelTestHooks.php

<?php

declare (strict_types=1);
namespace Drupal\mail_cancel_test\Hook;

use Drupal\Core\Hook\Attribute\Hook;

/**
 * Hook implementations for mail_cancel_test.
 */
class MailCancelTestHooks {
    
    /**
     * Implements hook_mail_alter().
     *
     * Aborts sending of messages with ID 'mail_cancel_test_cancel_test'.
     *
     * @see MailTestCase::testCancelMessage()
     */
    public function mailAlter(&$message) : void {
        if ($message['id'] == 'mail_cancel_test_cancel_test') {
            $message['send'] = FALSE;
        }
    }

}