Use different content fetching for SF6 and earlier

.gitignore

@@ -16,3 +16,6 @@
 /behat.yml
 /phpunit.xml
 /phpspec.yml
+
+/docker/
+node_modules

docker-compose.yml

@@ -0,0 +1,15 @@
+version: '3'
+services:
+    db:
+        image: mariadb:10.6
+        environment:
+            - MYSQL_DATABASE=sylius
+            - MYSQL_ROOT_PASSWORD=root
+            - MYSQL_USER=root
+            - MYSQL_PASSWORD=root
+            - MYSQL_ROOT_HOST=%
+        command: --sql_mode=""
+        ports:
+            - "3306:3306"
+        volumes:
+            - ./docker/volumes/mysql:/var/lib/mysql

tests/Controller/XmlApiTestCase.php

@@ -11,6 +11,7 @@
 use Symfony\Bundle\FrameworkBundle\Console\Application;
 use Symfony\Component\Console\Tester\CommandTester;
 use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\HttpKernel\Kernel;
 
 abstract class XmlApiTestCase extends BaseXmlApiTestCase
 {
@@ -34,13 +35,22 @@ protected function generateSitemaps(): void
 
     protected function getResponse(string $uri): Response
     {
-        $this->client->request('GET', $uri);
+        if (version_compare(Kernel::VERSION, '6.0', '>=')) {
+            $this->doRequest($uri);
+
+            return new Response(
+                $this->client->getInternalResponse()->getContent(),
+                $this->client->getInternalResponse()->getStatusCode(),
+                $this->client->getInternalResponse()->getHeaders(),
+            );
+        }
+
+        \ob_start();
+        $this->doRequest($uri);
+        $response = $this->client->getResponse();
+        $contents = \ob_get_clean();
 
-        return new Response(
-            $this->client->getInternalResponse()->getContent(),
-            $this->client->getInternalResponse()->getStatusCode(),
-            $this->client->getInternalResponse()->getHeaders(),
-        );
+        return new Response($contents, $response->getStatusCode(), $response->headers->all());
     }
 
     protected function deleteSitemaps(): void
@@ -64,4 +74,9 @@ protected function deleteSitemaps(): void
             }
         }
     }
+
+    private function doRequest(string $uri): void
+    {
+        $this->client->request('GET', $uri);
+    }
 }