diff --git a/core/modules/system/tests/modules/menu_test/menu_test.module b/core/modules/system/tests/modules/menu_test/menu_test.module
index 695c216..b0fdfe4 100644
--- a/core/modules/system/tests/modules/menu_test/menu_test.module
+++ b/core/modules/system/tests/modules/menu_test/menu_test.module
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Dummy module implementing hook menu.
+ * Test module providing tests for several menu related hooks.
  */
 
 use Drupal\menu_link\Plugin\Core\Entity\MenuLink;
@@ -33,12 +33,14 @@ function menu_test_menu() {
     'file' => 'system.admin.inc',
     'file path' => drupal_get_path('module', 'system'),
   );
+  // This item tests the description key.
   $items['menu_callback_description/description-plain'] = array(
     'title' => 'Menu item with a regular description',
     'page callback' => 'menu_test_callback',
     'description' => 'Menu item description text',
     'access arguments' => array('access content'),
   );
+  // This item tests using a description callback.
   $items['menu_callback_description/description-callback'] = array(
     'title' => 'Menu item with a description set with a callback',
     'page callback' => 'menu_test_callback',
@@ -204,7 +206,7 @@ function menu_test_menu() {
   );
 
   // Breadcrumbs tests.
-  // @see BreadcrumbTest
+  // @see Drupal\system\Tests\Menu\BreadcrumbTest
   $base = array(
     'page callback' => 'menu_test_callback',
     'access callback' => TRUE,
@@ -271,7 +273,7 @@ function menu_test_menu() {
   ) + $base;
 
   // Menu trail tests.
-  // @see MenuTrailTestCase
+  // @see Drupal\system\Tests\Menu\TrailTest
   $items['menu-test/menu-trail'] = array(
     'title' => 'Menu trail - Case 1',
     'page callback' => 'menu_test_menu_trail_callback',
@@ -308,13 +310,13 @@ function menu_test_menu() {
     'page callback' => 'menu_test_callback',
     'access arguments' => array('access content'),
   );
-
+  // Test the access key with a function callback.
   $items['menu_login_callback'] = array(
     'title' => 'Used as a login path',
     'page callback' => 'menu_login_callback',
     'access callback' => TRUE,
   );
-
+  // Test the access key.
   $items['menu-title-test/case1'] = array(
    'title' => 'Example title - Case 1',
    'access callback' => TRUE,
@@ -421,6 +423,9 @@ function menu_test_menu() {
 
 /**
  * Implements hook_menu_local_tasks().
+ * 
+ * If the menu_test.settings configuration 'tasks.add' has been set, adds 
+ * several local tasks to menu-test/tasks.
  */
 function menu_test_menu_local_tasks(&$data, $router_item, $root_path) {
   if (!config('menu_test.settings')->get('tasks.add')) {
@@ -448,6 +453,9 @@ function menu_test_menu_local_tasks(&$data, $router_item, $root_path) {
 
 /**
  * Implements hook_menu_local_tasks_alter().
+ *
+ * If the menu_test.settings configuration 'tasks.alter' has been set, adds 
+ * several local tasks to menu-test/tasks.
  */
 function menu_test_menu_local_tasks_alter(&$data, $router_item, $root_path) {
   if (!config('menu_test.settings')->get('tasks.alter')) {
@@ -487,14 +495,14 @@ function menu_test_other_argument_load($arg1) {
  * Dummy callback for hook_menu() to point to.
  *
  * @return
- *  A random string.
+ *   A text string which can be used for comparison.
  */
 function menu_test_callback() {
   return 'This is menu_test_callback().';
 }
 
 /**
- * Callback that test menu_test_menu_tree_set_path().
+ * Callback that tests menu_test_menu_tree_set_path().
  */
 function menu_test_menu_trail_callback() {
   $menu_path = state()->get('menu_test.menu_tree_set_path') ?: array();
@@ -508,7 +516,7 @@ function menu_test_menu_trail_callback() {
  * Implements hook_init().
  */
 function menu_test_init() {
-  // When requested by one of the MenuTrailTestCase tests, record the initial
+  // When requested by one of the TrailTest tests, record the initial
   // active trail during Drupal's bootstrap (before the user is redirected to a
   // custom 403 or 404 page). See menu_test_custom_403_404_callback().
   if (state()->get('menu_test.record_active_trail') ?: FALSE) {
@@ -518,9 +526,12 @@ function menu_test_init() {
 
 /**
  * Callback for our custom 403 and 404 pages.
+ *
+ * @return
+ *   A text string which can be used for comparison.
  */
 function menu_test_custom_403_404_callback() {
-  // When requested by one of the MenuTrailTestCase tests, record the final
+  // When requested by one of the TrailTest tests, record the final
   // active trail now that the user has been redirected to the custom 403 or
   // 404 page. See menu_test_init().
   if (state()->get('menu_test.record_active_trail') ?: FALSE) {
@@ -581,15 +592,13 @@ function menu_test_theme_callback($argument) {
 }
 
 /**
- * Implement hook_custom_theme().
+ * Implements hook_custom_theme().
  *
- * @return
- *   The name of the custom theme to use for the current page.
+ * If an appropriate variable has been set in the database, request the theme
+ * that is stored there. Otherwise, do not attempt to dynamically set the
+ * theme.
  */
 function menu_test_custom_theme() {
-  // If an appropriate variable has been set in the database, request the theme
-  // that is stored there. Otherwise, do not attempt to dynamically set the
-  // theme.
   if ($theme = state()->get('menu_test.hook_custom_theme_name') ?: FALSE) {
     return $theme;
   }
@@ -614,9 +623,6 @@ function menu_test_menu_name($new_name = '') {
 
 /**
  * Implements hook_menu_link_insert().
- *
- * @return
- *  A random string.
  */
 function menu_test_menu_link_insert(MenuLink $item) {
   menu_test_static_variable('insert');
@@ -624,9 +630,6 @@ function menu_test_menu_link_insert(MenuLink $item) {
 
 /**
  * Implements hook_menu_link_update().
- *
- * @return
- *  A random string.
  */
 function menu_test_menu_link_update(MenuLink $item) {
   menu_test_static_variable('update');
@@ -634,9 +637,6 @@ function menu_test_menu_link_update(MenuLink $item) {
 
 /**
  * Implements hook_menu_link_delete().
- *
- * @return
- *  A random string.
  */
 function menu_test_menu_link_delete(MenuLink $item) {
   menu_test_static_variable('delete');
@@ -662,7 +662,7 @@ function menu_test_static_variable($value = NULL) {
  * Implements hook_menu_site_status_alter().
  */
 function menu_test_menu_site_status_alter(&$menu_site_status, $path) {
-  // Allow access to menu_login_callback even if in maintenance mode.
+  // Allow access to menu_login_callback() even if in maintenance mode.
   if ($menu_site_status == MENU_SITE_OFFLINE && $path == 'menu_login_callback') {
     $menu_site_status = MENU_SITE_ONLINE;
   }
@@ -670,6 +670,9 @@ function menu_test_menu_site_status_alter(&$menu_site_status, $path) {
 
 /**
  * Menu callback to be used as a login path.
+ *
+ * @return
+ *   A text string which can be used for comparison.
  */
 function menu_login_callback() {
   return 'This is menu_login_callback().';