diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 493fa32..bc62f1b 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -1433,9 +1433,6 @@ function drupal_serve_page_from_cache(stdClass $cache) {
   // fields that fully determines whether a cache is permitted to use the
   // response to reply to a subsequent request for a given URL without
   // revalidation.
-  debug(123);
-  debug($boot_headers['vary']);
-  debug(settings()->get('omit_vary_cookie'));
   if (!isset($boot_headers['vary']) && !settings()->get('omit_vary_cookie')) {
     header('Vary: Cookie');
   }
diff --git a/core/lib/Drupal/Component/Utility/Settings.php b/core/lib/Drupal/Component/Utility/Settings.php
index 57cc416..eb59e66 100644
--- a/core/lib/Drupal/Component/Utility/Settings.php
+++ b/core/lib/Drupal/Component/Utility/Settings.php
@@ -78,18 +78,4 @@ public function getAll() {
     return $this->storage;
   }
 
-  /**
-   * Set a value in the setting, NEVER use this unless you know what you do.
-   *
-   * Use the settings.php unless you write a test for a setting.
-   *
-   * @param string $name
-   *   The name of the setting to change.
-   * @param mixed $value
-   *   The new value of the setting.
-   */
-  public function set($name, $value) {
-    $this->storage[$name] = $value;
-  }
-
 }
diff --git a/core/modules/system/lib/Drupal/system/Tests/Bootstrap/PageCacheTest.php b/core/modules/system/lib/Drupal/system/Tests/Bootstrap/PageCacheTest.php
index 6b4a033..8ee5bba 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Bootstrap/PageCacheTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Bootstrap/PageCacheTest.php
@@ -41,7 +41,7 @@ function setUp() {
   /**
    * Tests support of requests with If-Modified-Since and If-None-Match headers.
    */
-  function _testConditionalRequests() {
+  function testConditionalRequests() {
     $config = config('system.performance');
     $config->set('cache.page.use_internal', 1);
     $config->set('cache.page.max_age', 300);
@@ -126,12 +126,13 @@ function testPageCache() {
 
     // Check the omit_vary_cookie setting.
     $this->drupalLogout();
-    // Remove the page cache in order to hit the uncached page.
-    cache('page')->deleteAll();
-    settings()->set('omit_vary_cookie', TRUE);
+    $settings['settings']['omit_vary_cookie'] = (object) array(
+      'value' => TRUE,
+      'required' => TRUE,
+    );
+    $this->writeSettings($settings);
     $this->drupalGet('system-test/set-header', array('query' => array('name' => 'Foo', 'value' => 'bar')));
     $this->assertTrue(strpos($this->drupalGetHeader('Vary'), 'Cookie') === FALSE, 'Vary: Cookie header was not sent.');
-    $this->container->get('settings')->set('omit_vary_cookie', FALSE);
   }
 
   /**
@@ -141,7 +142,7 @@ function testPageCache() {
    * .htaccess or similar, or if compression is done outside PHP, e.g. by the
    * mod_deflate Apache module.
    */
-  function _testPageCompression() {
+  function testPageCompression() {
     $config = config('system.performance');
     $config->set('cache.page.use_internal', 1);
     $config->set('cache.page.max_age', 300);