cakephp/tests/test_app/TestApp/Http/TestRequestHandler.php

<?php
declare(strict_types=1);

/**
 * CakePHP(tm) : Rapid Development Framework (https://cakephp.org)
 * Copyright (c) Cake Software Foundation, Inc. (https://cakefoundation.org)
 * Licensed under The MIT License
 * For full copyright and license information, please see the LICENSE.txt
 * Redistributions of files must retain the above copyright notice.
 *
 * @copyright     Copyright (c) Cake Software Foundation, Inc. (https://cakefoundation.org)
 * @link          https://cakephp.org CakePHP(tm) Project
 * @license       https://www.opensource.org/licenses/mit-license.php MIT License
 */
namespace TestApp\Http;

use Cake\Http\Response;
use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Server\RequestHandlerInterface;

class TestRequestHandler implements RequestHandlerInterface
{
    public $callable;

    public function __construct(?callable $callable = null)
    {
        $this->callable = $callable ?: function ($request) {
            return new Response();
        };
    }

    public function handle(ServerRequestInterface $request): ResponseInterface
    {
        return ($this->callable)($request);
    }
}