Add a missing property

Closes #3436885

tests/tfa.test

@@ -10,6 +10,13 @@
  */
 class TfaTestCase extends DrupalWebTestCase {
 
+  /**
+   * A user with permission to access content.
+   *
+   * @var object
+   */
+  protected $web_user;
+
   /**
    * Implement getInfo().
    */