Issue #1950684 by Berdir: Fixed Mock and protect ['user'] in DUTB tests.

core/modules/simpletest/lib/Drupal/simpletest/TestBase.php

@@ -867,6 +867,9 @@ protected function prepareEnvironment() {
 
     // Ensure that the current session is not changed by the new environment.
     drupal_save_session(FALSE);
+    // Run all tests as a anonymous user by default, web tests will replace that
+    // during the test set up.
+    $user = drupal_anonymous_user();
 
     // 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

core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php

@@ -775,10 +775,6 @@ protected function setUp() {
       ),
     );
 
-    // 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();