diff --git a/core/lib/Drupal/Core/Controller/ControllerBase.php b/core/lib/Drupal/Core/Controller/ControllerBase.php
index fb0f1d4..389279a 100644
--- a/core/lib/Drupal/Core/Controller/ControllerBase.php
+++ b/core/lib/Drupal/Core/Controller/ControllerBase.php
@@ -15,12 +15,12 @@
  *
  * Controllers that use this base class have access to a number of utility
  * methods and to the Container, which can greatly reduce boilerplate dependency
- * handling code.  However, it also renders the class impossible to unit test.
- * Therefore this base class should only be used by controller classes that
- * contain only trivial glue code.  Controllers that contain sufficiently
- * complex logic that it's worth testing should not use this base class but
- * use ControllerInterface instead, or even better be refactored to be trivial
- * glue code.
+ * handling code.  However, it also makes the class considerably more
+ * difficult to unit test. Therefore this base class should only be used by
+ * controller classes that contain only trivial glue code.  Controllers that
+ * contain sufficiently complex logic that it's worth testing should not use
+ * this base class but use ControllerInterface instead, or even better be
+ * refactored to be trivial glue code.
  *
  * The services exposed here are those that it is reasonable for a well-behaved
  * controller to leverage. A controller that needs other other services may
@@ -56,19 +56,6 @@ protected function cache($bin = 'cache') {
   }
 
   /**
-   * Returns an expirable key value store collection.
-   *
-   * @param string $collection
-   *   The name of the collection holding key and value pairs.
-   *
-   * @return \Drupal\Core\KeyValueStore\KeyValueStoreExpirableInterface
-   *   An expirable key value store collection.
-   */
-  protected function keyValueExpirable($collection) {
-    return $this->container->get('keyvalue.expirable')->get($collection);
-  }
-
-  /**
    * Retrieves a configuration object.
    *
    * This is the main entry point to the configuration API. Calling
diff --git a/core/lib/Drupal/Core/Controller/ControllerInterface.php b/core/lib/Drupal/Core/Controller/ControllerInterface.php
index c490f9c..5cdab2e 100644
--- a/core/lib/Drupal/Core/Controller/ControllerInterface.php
+++ b/core/lib/Drupal/Core/Controller/ControllerInterface.php
@@ -17,8 +17,8 @@
  * a lot of boilerplate code in the class. As an alternative, controllers that
  * contain only limited glue code ("thin" controllers) should instead extend
  * ControllerBase as that allows direct access to the container. That renders
- * the controller un-unit-testable so should only be used for controllers that
- * are trivial in complexity.
+ * the controller very difficult to unit test so should only be used for
+ * controllers that are trivial in complexity.
  */
 interface ControllerInterface {