Fatal error: Uncaught Error: Class "PHPUnit\Framework\Constraint\Constraint" not found in /opt/lampp/htdocs/forum/flarum/vendor/symfony/http-foundation/Test/Constraint/ResponseHasHeader.php:17 Stack trace: #0 {main} thrown in /opt/lampp/htdocs/forum/flarum/vendor/symfony/http-foundation/Test/Constraint/ResponseHasHeader.php on line 17