diff --git a/core/modules/aggregator/src/Tests/AggregatorTestBase.php b/core/modules/aggregator/src/Tests/AggregatorTestBase.php
index 616e1e2..cf845db 100644
--- a/core/modules/aggregator/src/Tests/AggregatorTestBase.php
+++ b/core/modules/aggregator/src/Tests/AggregatorTestBase.php
@@ -136,7 +136,7 @@ function getFeedEditObject($feed_url = NULL, array $values = array()) {
    */
   function getDefaultFeedItemCount() {
     // Our tests are based off of rss.xml, so let's find out how many elements should be related.
-    $feed_count = db_query_range('SELECT COUNT(DISTINCT nid) FROM {node_field_data} n WHERE n.promote = 1 AND n.status = 1', 0, $this->container->get('config.factory')->get('system.rss')->get('items.limit'))->fetchField();
+    $feed_count = db_query_range('SELECT COUNT(DISTINCT nid) FROM {node_field_data} n WHERE n.promote = 1 AND n.status = 1', 0, $this->config('system.rss')->get('items.limit'))->fetchField();
     return $feed_count > 10 ? 10 : $feed_count;
   }
 
@@ -336,7 +336,7 @@ function createSampleNodes($count = 5) {
    * Enable the plugins coming with aggregator_test module.
    */
   function enableTestPlugins() {
-    $this->container->get('config.factory')->get('aggregator.settings')
+    $this->config('aggregator.settings')
       ->set('fetcher', 'aggregator_test_fetcher')
       ->set('parser', 'aggregator_test_parser')
       ->set('processors', array(
diff --git a/core/modules/locale/src/Tests/LocaleConfigTranslationImportTest.php b/core/modules/locale/src/Tests/LocaleConfigTranslationImportTest.php
index ae914d8..cacf88d 100644
--- a/core/modules/locale/src/Tests/LocaleConfigTranslationImportTest.php
+++ b/core/modules/locale/src/Tests/LocaleConfigTranslationImportTest.php
@@ -36,7 +36,7 @@ protected function setUp() {
 
     // Update module should not go out to d.o to check for updates. We override
     // the url to an invalid update source. No update data will be found.
-    \Drupal::config('update.settings')->set('fetch.url', (string) Url::fromRoute('<front>', array(), array('absolute' => TRUE)))->save();
+    $this->config('update.settings')->set('fetch.url', (string) Url::fromRoute('<front>', array(), array('absolute' => TRUE)))->save();
   }
 
   /**
@@ -54,7 +54,7 @@ public function testConfigTranslationImport() {
 
     // Enable import of translations. By default this is disabled for automated
     // tests.
-    \Drupal::config('locale.settings')
+    $this->config('locale.settings')
       ->set('translation.import_enabled', TRUE)
       ->save();
 
diff --git a/core/modules/system/src/Tests/Mail/MailTest.php b/core/modules/system/src/Tests/Mail/MailTest.php
index c82a152..3603332 100644
--- a/core/modules/system/src/Tests/Mail/MailTest.php
+++ b/core/modules/system/src/Tests/Mail/MailTest.php
@@ -48,7 +48,7 @@ public function testPluggableFramework() {
     $this->assertTrue($mail_backend instanceof TestPhpMailFailure, 'Default mail interface can be swapped.');
 
     // Add a module-specific mail backend.
-    \Drupal::config('system.mail')->set('interface.mymodule_testkey', 'test_mail_collector')->save();
+    $this->config('system.mail')->set('interface.mymodule_testkey', 'test_mail_collector')->save();
 
     // Get the added MailInterface class instance.
     $mail_backend = \Drupal::service('plugin.manager.mail')->getInstance(array('module' => 'mymodule', 'key' => 'testkey'));
diff --git a/core/modules/tour/src/Tests/TourTestBasic.php b/core/modules/tour/src/Tests/TourTestBasic.php
index 5cf9322..160f782 100644
--- a/core/modules/tour/src/Tests/TourTestBasic.php
+++ b/core/modules/tour/src/Tests/TourTestBasic.php
@@ -50,8 +50,7 @@ protected function setUp() {
     // Make sure we are using distinct default and administrative themes for
     // the duration of these tests.
     $this->container->get('theme_handler')->install(array('bartik', 'seven'));
-    $this->container->get('config.factory')
-      ->get('system.theme')
+    $this->config('system.theme')
       ->set('default', 'bartik')
       ->set('admin', 'seven')
       ->save();
diff --git a/core/tests/Drupal/Tests/Core/DrupalTest.php b/core/tests/Drupal/Tests/Core/DrupalTest.php
index 4af023d..8a36cfd 100644
--- a/core/tests/Drupal/Tests/Core/DrupalTest.php
+++ b/core/tests/Drupal/Tests/Core/DrupalTest.php
@@ -133,6 +133,7 @@ public function testConfig() {
       ->will($this->returnValue(TRUE));
     $this->setMockContainerService('config.factory', $config);
 
+    // Test \Drupal::config(), not $this->config().
     $this->assertNotNull(\Drupal::config('test_config'));
   }