diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index 6ace8a8..9e68690 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -987,9 +987,6 @@ protected function writeCustomTranslations() {
     foreach ($this->customTranslations as $langcode => $values) {
       $settings_key = 'locale_custom_strings_' . $langcode;
 
-      // Update in-memory settings directly.
-      $this->settingsSet($settings_key, $values);
-
       $settings['settings'][$settings_key] = (object) array(
         'value' => $values,
         'required' => TRUE,
diff --git a/core/modules/system/src/Tests/Common/FormatDateTest.php b/core/modules/system/src/Tests/Common/FormatDateTest.php
index 33a7f91..abdfa93 100644
--- a/core/modules/system/src/Tests/Common/FormatDateTest.php
+++ b/core/modules/system/src/Tests/Common/FormatDateTest.php
@@ -43,7 +43,7 @@ protected function setUp() {
     $formats['short']->setPattern('Y M j - g:ia')->save();
     $this->refreshVariables();
 
-    $this->settingsSet('locale_custom_strings_' . self::LANGCODE, array(
+    $this->writeSettings('locale_custom_strings_' . self::LANGCODE, array(
       '' => array('Sunday' => 'domingo'),
       'Long month name' => array('March' => 'marzo'),
     ));
diff --git a/core/modules/system/src/Tests/Session/SessionTest.php b/core/modules/system/src/Tests/Session/SessionTest.php
index 632cbcd..46b60df 100644
--- a/core/modules/system/src/Tests/Session/SessionTest.php
+++ b/core/modules/system/src/Tests/Session/SessionTest.php
@@ -242,7 +242,7 @@ function testSessionWrite() {
     $this->assertEqual($times4->timestamp, $times3->timestamp, 'Sessions table was not updated.');
 
     // Force updating of users and sessions table once per second.
-    $this->settingsSet('session_write_interval', 0);
+    $this->writeSettings('session_write_interval', 0);
     // Write that value also into the test settings.php file.
     $settings['settings']['session_write_interval'] = (object) array(
       'value' => 0,