diff --git a/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php b/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
index 4d50933..d1c62c6 100644
--- a/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
+++ b/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
@@ -126,9 +126,7 @@ public function scan($type, $include_tests = NULL) {
     // Unless an explicit value has been passed, manually check whether we are
     // in a test environment, in which case test extensions must be included.
     if (!isset($include_tests)) {
-      // @todo Replace with drupal_valid_test_ua() once avaiable.
-      // @see https://drupal.org/node/2171683
-      $include_tests = !empty($GLOBALS['drupal_test_info']['test_run_id']);
+      $include_tests = (bool) drupal_valid_test_ua();
     }
 
     $files = array();