diff --git a/core/modules/system/lib/Drupal/system/Tests/Common/RenderTest.php b/core/modules/system/lib/Drupal/system/Tests/Common/RenderTest.php
index 14ce926..bd388a6 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Common/RenderTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Common/RenderTest.php
@@ -858,7 +858,7 @@ function testDrupalRenderRenderCachePlaceholder() {
    * element.
    */
   function testDrupalRenderChildElementRenderCachePlaceholder() {
-    $context = array('bar' => $this->randomString());
+    $context = array('bar' => $this->randomContextValue());
     $container = array(
       '#type' => 'container',
     );
diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index 25a6933..d8330f1 100755
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -71,11 +71,17 @@
 
 simpletest_script_reporter_init();
 
-// Execute tests.
+$args['repeat'] = 400;
+$test_list = array('\Drupal\system\Tests\Common\RenderTest');
+$tests_to_run = array();
 for ($i = 0; $i < $args['repeat']; $i++) {
-  simpletest_script_execute_batch($test_list);
+  $tests_to_run = array_merge($tests_to_run, $test_list);
 }
 
+// Execute tests.
+simpletest_script_execute_batch($tests_to_run);
+
+
 // Stop the timer.
 simpletest_script_reporter_timer_stop();