-if (false === getenv('SYMFONY_PHPUNIT_DIR')) {
-    putenv('SYMFONY_PHPUNIT_DIR='.__DIR__.'/.phpunit');
-}
+if (is_file(dirname(__DIR__).'/vendor/phpunit/phpunit/phpunit')) {
+    if (PHP_VERSION_ID >= 80000) {
+        require dirname(__DIR__).'/vendor/phpunit/phpunit/phpunit';
+    } else {
+        define('PHPUNIT_COMPOSER_INSTALL', dirname(__DIR__).'/vendor/autoload.php');
+        require PHPUNIT_COMPOSER_INSTALL;
+        PHPUnit\TextUI\Command::main();
+    }
+} else {
+    if (!is_file(dirname(__DIR__).'/vendor/symfony/phpunit-bridge/bin/simple-phpunit.php')) {
+        echo "Unable to find the `simple-phpunit.php` script in `vendor/symfony/phpunit-bridge/bin/`.\n";
+        exit(1);
+    }