output_test_listener.php

<?php

namespace App\Debug;

use Symfony\Component\HttpKernel\Event\ResponseEvent;
use Symfony\Component\EventDispatcher\Attribute\AsEventListener;
use Symfony\Component\DependencyInjection\Attribute\When;

#[When(env: 'test')]
#[AsEventListener]
final class OutputContentListener
{
    private string $logDir;

    public function __construct(string $logDir)
    {
        $this->logDir = $logDir;
    }

    public function __invoke(ResponseEvent $event): void
    {
        $request = $event->getRequest();
        $response = $event->getResponse();

        $contentType = $response->headers->get('content-type');
        $content = $response->getContent();

        if (null !== $contentType && str_ends_with($contentType, 'json')) {
            $suffix = 'json';
        } else {
            $suffix = $content !== strip_tags($content) ? 'html' : 'txt';
        }

        $logDir = $this->logDir.'/responses';
        if (false === file_exists($logDir)) {
            mkdir($logDir);
        }

        $fileName = str_replace("/", "_", substr($request->getRequestUri(), 1));

        file_put_contents(sprintf("%s/%s_%s.%s", $logDir, strtolower($request->getMethod()), $fileName, $suffix), $content);
    }
}

Don't forget to bind $logDir in services.yaml

        bind:
            $logDir: "%kernel.logs_dir%"