diff -u b/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
--- b/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -48,19 +48,7 @@
 
-$autoloader = require_once __DIR__ . '/../../autoload.php';
-
 if (!class_exists(TestCase::class)) {
   echo "\nrun-tests.sh requires the PHPUnit testing framework. Please use 'composer install --dev' to ensure that it is present.\n\n";
   exit(SIMPLETEST_SCRIPT_EXIT_FAILURE);
 }
 
-try {
-  $request = Request::createFromGlobals();
-  $kernel = TestRunnerKernel::createFromRequest($request, $autoloader);
-  $kernel->prepareLegacyRequest($request);
-}
-catch (Exception $e) {
-  echo (string) $e;
-  exit(SIMPLETEST_SCRIPT_EXIT_EXCEPTION);
-}
-
 if ($args['execute-test']) {
@@ -485,6 +473,8 @@
     passthru("$composer run-script drupal-phpunit-upgrade-check");
   }
 
+  $autoloader = require_once __DIR__ . '/../../autoload.php';
+
   // Get URL from arguments.
   if (!empty($args['url'])) {
     $parsed_url = parse_url($args['url']);
@@ -543,6 +533,17 @@
   }
 
   chdir(realpath(__DIR__ . '/../..'));
+
+  // Prepare the kernel.
+  try {
+    $request = Request::createFromGlobals();
+    $kernel = TestRunnerKernel::createFromRequest($request, $autoloader);
+    $kernel->prepareLegacyRequest($request);
+  }
+  catch (Exception $e) {
+    echo (string) $e;
+    exit(SIMPLETEST_SCRIPT_EXIT_EXCEPTION);
+  }
 }
 
 /**