Magento 2 : Script for Quick Test purpose

test.php

<?php
require __DIR__ . '/app/bootstrap.php';
$bootstrap = \Magento\Framework\App\Bootstrap::create(BP, $_SERVER);
/** @var \Magento\Framework\App\Http $app */
$app = $bootstrap->createApplication('TestApp');
$bootstrap->run($app);

testApp.php

<?php

use Magento\Framework\App\Bootstrap;

class TestApp extends \Magento\Framework\App\Http implements \Magento\Framework\AppInterface
{
    public function launch()
    {

        echo 'test';
        
        //the method must end with this line
        return $this->_response;
    }

    /**
     * @inheritdoc
     */
    public function catchException(Bootstrap $bootstrap, \Exception $exception): bool
    {
        return false;
    }

}