diff --git a/core/lib/Drupal/Core/Extension/ThemeHandler.php b/core/lib/Drupal/Core/Extension/ThemeHandler.php
index 25784ca..dbe2c78 100644
--- a/core/lib/Drupal/Core/Extension/ThemeHandler.php
+++ b/core/lib/Drupal/Core/Extension/ThemeHandler.php
@@ -133,10 +133,8 @@ public function getDefault() {
    * {@inheritdoc}
    */
   public function setDefault($name) {
-    if (!isset($this->list)) {
-      $this->listInfo();
-    }
-    if (!isset($this->list[$name])) {
+    $list = $this->listInfo();
+    if (!isset($list[$name])) {
       throw new \InvalidArgumentException("$name theme is not enabled.");
     }
     $this->configFactory->get('system.theme')
@@ -275,10 +273,11 @@ public function enable(array $theme_list, $enable_dependencies = TRUE) {
    * {@inheritdoc}
    */
   public function disable(array $theme_list) {
+    $list = $this->listInfo();
     $theme_config = $this->configFactory->get('system.theme');
 
     foreach ($theme_list as $key) {
-      if (!isset($this->list[$key])) {
+      if (!isset($list[$key])) {
         throw new \InvalidArgumentException("Unknown theme: $key.");
       }
       if ($key === $theme_config->get('default')) {
@@ -289,9 +288,9 @@ public function disable(array $theme_list) {
       }
       // Base themes cannot be disabled if sub themes are enabled, and if they
       // are not disabled at the same time.
-      if (!empty($this->list[$key]->sub_themes)) {
-        foreach ($this->list[$key]->sub_themes as $sub_key => $sub_label) {
-          if (isset($this->list[$sub_key]) && !in_array($sub_key, $theme_list, TRUE)) {
+      if (!empty($list[$key]->sub_themes)) {
+        foreach ($list[$key]->sub_themes as $sub_key => $sub_label) {
+          if (isset($list[$sub_key]) && !in_array($sub_key, $theme_list, TRUE)) {
             throw new \InvalidArgumentException("The base theme $key cannot be disabled, because theme $sub_key depends on it.");
           }
         }
diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index 643bcb7..76d544a 100755
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -71,11 +71,17 @@
 
 simpletest_script_reporter_init();
 
-// Execute tests.
+$args['repeat'] = 200;
+$test_list = array('Drupal\config\Tests\ConfigImportUITest');
+
+$tests_to_run = array();
 for ($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();