ThemeTestPreprocess.php

<?php

declare (strict_types=1);
namespace Drupal\theme_test;


/**
 * Class to test preprocess callbacks.
 */
class ThemeTestPreprocess {
    
    /**
     * Preprocess callback for testing preprocess callbacks.
     *
     * @param array $variables
     *   An associative array containing:
     *   - foo: Text for testing preprocess callback.
     */
    public static function preprocess(&$variables) {
        $variables['foo'] = 'Make Drupal full of kittens again!';
    }

}