diff --git a/core/lib/Drupal/Core/Session/AccountProxy.php b/core/lib/Drupal/Core/Session/AccountProxy.php
index 8e85cf2..cb6fbd2 100644
--- a/core/lib/Drupal/Core/Session/AccountProxy.php
+++ b/core/lib/Drupal/Core/Session/AccountProxy.php
@@ -126,7 +126,7 @@ public function revertAccount() {
       $this->account = array_pop($this->accountStack);
     }
     else {
-      throw new \RuntimeException(t('No more account impersonations to revert.'));
+      throw new \RuntimeException('No more account impersonations to revert.');
     }
     // Restore original session saving status if all impersonations are reverted.
     if (empty($this->accountStack)) {
@@ -147,7 +147,7 @@ public function revertAll() {
       $this->accountStack = array();
     }
     else {
-      throw new \RuntimeException(t('No more account impersonations to revert.'));
+      throw new \RuntimeException('No more account impersonations to revert.');
     }
     // Restore original session saving status if all impersonations are reverted.
     if ($this->originalSessionSaving) {
diff --git a/core/modules/system/lib/Drupal/system/Tests/Session/UserImpersonatingUserTest.php b/core/modules/system/src/Tests/Session/UserImpersonatingUserTest.php
similarity index 87%
rename from core/modules/system/lib/Drupal/system/Tests/Session/UserImpersonatingUserTest.php
rename to core/modules/system/src/Tests/Session/UserImpersonatingUserTest.php
index 7b715fa..2222e58 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Session/UserImpersonatingUserTest.php
+++ b/core/modules/system/src/Tests/Session/UserImpersonatingUserTest.php
@@ -2,19 +2,19 @@
 
 /**
  * @file
- * Contains Drupal\user\Tests\UserImpersonatingUserTest.
+ * Contains Drupal\system\Tests\Session\UserImpersonatingUserTest.
  */
 
 namespace Drupal\system\Tests\Session;
 
 use Drupal\Core\Session\AnonymousUserSession;
 use Drupal\Core\Session\UserSession;
-use Drupal\simpletest\WebTestBase;
+use Drupal\simpletest\KernelTestBase;
 
 /**
  * Test case for impersonating users.
  */
-class UserImpersonatingUserTest extends WebTestBase {
+class UserImpersonatingUserTest extends KernelTestBase {
 
   public static function getInfo() {
     return array(
@@ -28,8 +28,7 @@ function testUserImpersonateUser() {
     $session_manager = $this->container->get('session_manager');
     $user = $this->container->get('current_user');
     $original_user = clone $user;
-    $this->verbose('Session saving status: '. var_dump($session_manager->isEnabled()));
-    $this->assertFalse($session_manager->isEnabled(), 'Session saving is initially disabled.');
+    $original_session_saving = $session_manager->isEnabled();
 
     // If not currently logged in, use AccountProxy::impersonateAccount() to switch to
     // user 1. If logged in, switch to the anonymous user instead.
@@ -67,8 +66,8 @@ function testUserImpersonateUser() {
 
     // Assert that the original user is the active user again, and that session
     // saving has been re-enabled.
-    $this->assertEqual($user->id(), $original_user->id(), 'Original user successfully restored.');
-    $this->assertTrue($session_manager->isEnabled(), 'Session saving is enabled.');
+    $this->assertEqual($user->id(), $original_user->id(), 'Original user correctly restored.');
+    $this->assertEqual($session_manager->isEnabled(), $original_session_saving, 'Original session saving correctly restored.');
 
     // Verify that AccountProxy::revertAccount and AccountProxy::revertAll()
     // will throw exceptions if there is none left in the stack.