diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 611e4794ed..65c3f4a116 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -80,10 +80,10 @@ function system_requirements($phase) {
     $requirements['simpletest_enabled'] = [
       'title' => t('Testing module'),
       'value' => t('Not enabled'),
-      'description' => t('The Testing/simpletest module should not be enabled on production sites, because it represents a security risk.'),
+      'description' => t('The Testing module should not be enabled on production sites, because it represents a <a href=":url">security risk</a>.', [':url' => 'https://www.drupal.org/docs/8/security/secure-configuration-for-site-builders']),
       'severity' => REQUIREMENT_OK,
     ];
-    if (array_key_exists('simpletest', $enabled_modules)) {
+    if (isset($enabled_modules['simpletest'])) {
       $requirements['simpletest_enabled']['value'] = t('Enabled');
       $requirements['simpletest_enabled']['severity'] = REQUIREMENT_WARNING;
     }