diff -u b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
--- b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
@@ -639,4 +639,7 @@
     $this->originalUser = clone $user;
 
+    // Ensure that the current session is not changed by the new environment.
+    drupal_save_session(FALSE);
+
     // Save and clean the shutdown callbacks array because it is static cached
     // and will be changed by the test run. Otherwise it will contain callbacks
diff -u b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
--- b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -609,9 +609,8 @@
     // @see drupal_system_listing()
     $conf['simpletest_parent_profile'] = $this->originalProfile;
 
-    // Run the Drupal installer non-interactively.
+    // Set installer parameters.
     // @see install.php, install.core.inc
-    require_once DRUPAL_ROOT . '/core/includes/install.core.inc';
     $connection_info = Database::getConnectionInfo('default');
     $this->root_user = (object) array(
       'name' => 'admin',
@@ -653,22 +652,20 @@
       ),
     );
 
-    // Reset the batch and invoke the non-interactive installer.
-    $batch = &batch_get();
-    $batch = array();
-
-    // Ensure that the session is not changed by the new environment.
-    drupal_save_session(FALSE);
-
     // Replace the global $user session with an anonymous user to resemble a
     // regular installation.
     $user = drupal_anonymous_user();
 
+    // Reset the static batch to remove Simpletest's batch operations.
+    $batch = &batch_get();
+    $batch = array();
+
     // The installer sets/overrides some services to Null implementations, since
     // there is no database yet. Thus, backup and restore the current $conf.
     $originalConf = $conf;
-    
+
     // Execute the non-interactive installer.
+    require_once DRUPAL_ROOT . '/core/includes/install.core.inc';
     install_drupal($settings);
 
     // Restore global $conf from before install_begin_request().