cakephp/tests/test_app/TestApp/Controller/ControllerTestAppController.php

<?php
declare(strict_types=1);
namespace TestApp\Controller;

use Cake\Controller\Controller;

/**
 * AppController class
 */
class ControllerTestAppController extends Controller
{
    /**
     * modelClass property
     *
     * @var string
     */
    public $modelClass = 'Posts';
}