Setter in Guzzle 5 is not allowed in Guzzle6 - php

Question

I'm using Guzzle to make tests on the API i'm working on in Symfony2.
I've been watching the knpUniversity series on Rest, and i have trouble updating the part where i should be able to use the app_test.php instead of app.php.
In the series, they use Guzzle v5, but in v6 there are major changes with PSR7 use
In the tutorial, to permit the use of another uri ending with other than app.php, they use :
use GuzzleHttp\Event\BeforeEvent;
...
class ApiTestCase extends KernelTestCase
{
...
public static function setUpBeforeClass()
{
$baseUrl = getenv('TEST_BASE_URL');
self::$staticClient = new Client([
'base_url' => $baseUrl,
'defaults' => [
'exceptions' => false
]
]);
...
// guaranteeing that /app_test.php is prefixed to all URLs
self::$staticClient->getEmitter()
->on('before', function(BeforeEvent $event) {
$path = $event->getRequest()->getPath();
if (strpos($path, '/api') === 0) {
$event->getRequest()->setPath('/app_test.php'.$path);
}
});
self::bootKernel();
}
But with Guzzle6, there is no setter for the request :
use GuzzleHttp\Client;
use GuzzleHttp\HandlerStack;
use GuzzleHttp\Middleware;
use Psr\Http\Message\RequestInterface;
use Psr\Http\Message\ResponseInterface;
use Symfony\Bundle\FrameworkBundle\Test\KernelTestCase;
class ApiTestCase extends KernelTestCase
{
private static $staticClient;
protected $client;
public static function setUpBeforeClass()
{
//defined in phpunit.xml
$baseUri = getenv('TEST_BASE_URI');
//Create a handler stack that has all of the default middlewares attached
$handler = HandlerStack::create();
// guaranteeing that /app_test.php is prefixed to all URLs
$handler->push(Middleware::mapRequest(function (RequestInterface $request) {
$path = $request->getUri()->getPath();
if (strpos($path, '/api') === 0) {
$request->getUri()->setPath('/app_test.php'.$path); // <-- this is not allowed
}
// Notice that we have to return a request object
return $request->withHeader('X-Foo', 'Bar');
}));
// Inject the handler into the client
self::$staticClient = new Client([
'base_uri' => $baseUri.'/app_test.php',
'handler' => $handler,
'defaults' => [
'http_errors' => false
]
]);
//Allows to use service container
self::bootKernel();
}
So how can i change the uri, to use the app_test.php instead of app.php ?
Thanks
===========================
EDIT :
Actually, they give a solution in one of the post of the comment
$handler->push(Middleware::mapRequest(function(RequestInterface $request) {
$path = $request->getUri()->getPath();
if (strpos($path, '/app_test.php') !== 0) {
$path = '/app_test.php' . $path;
}
$uri = $request->getUri()->withPath($path);
return $request->withUri($uri);
}));
Thanks #Cerad