diff --git a/core/modules/node/lib/Drupal/node/Tests/NodeAccessBaseTableTest.php b/core/modules/node/lib/Drupal/node/Tests/NodeAccessBaseTableTest.php
index adee17d..60bae75 100644
--- a/core/modules/node/lib/Drupal/node/Tests/NodeAccessBaseTableTest.php
+++ b/core/modules/node/lib/Drupal/node/Tests/NodeAccessBaseTableTest.php
@@ -125,7 +125,7 @@ function testNodeAccessBasic() {
       $this->assertTaxonomyPage(FALSE);
     }
 
-    // Now test that a user with 'access any private content' can view content.
+    // Now test that a user with 'node test view' permissions can view content.
     $access_user = $this->drupalCreateUser(array('access content', 'create article content', 'node test view', 'search content'));
     $this->drupalLogin($access_user);
 
diff --git a/core/modules/node/tests/modules/node_access_test/node_access_test.module b/core/modules/node/tests/modules/node_access_test/node_access_test.module
index ac25cb2..10e555e 100644
--- a/core/modules/node/tests/modules/node_access_test/node_access_test.module
+++ b/core/modules/node/tests/modules/node_access_test/node_access_test.module
@@ -2,17 +2,47 @@
 
 /**
  * @file
- * A dummy module implementing node access related hooks for testing purposes.
+ * Test module for testing the node access system.
  *
- * A dummy module implementing node access related hooks to test API interaction
- * with the Node module. This module restricts view permission to those with
- * a special 'node test view' permission.
+ * This module's functionality depends on two configuration variables:
+ * - node_access_test.no_access_uid: Used in NodeQueryAlterTest to enable the
+ *   node_access_all grant realm.
+ * - node_access_test.private: When TRUE, the module controls access for nodes
+ *   with a 'private' property set, and inherits the default core access for
+ *   nodes without this flag. When FALSE, the module controls access for all
+ *   nodes.
+ * - node_access_test_secret_catalan: When set to TRUE and using the Catalan
+ *   'ca' language code, makes all Catalan content secret.
+ *
+ * @see node_access_test_node_grants()
+ * @see \Drupal\node\Tests\NodeQueryAlterTest
+ * @see \Drupal\node\Tests\NodeAccessBaseTableTest
  */
 
 use Drupal\Core\Entity\EntityInterface;
 
 /**
  * Implements hook_node_grants().
+ *
+ * Provides three grant realms:
+ * - node_access_test_author: Grants users view, update, and delete privileges
+ *   on nodes they have authored. Users receive a group ID matching their user
+ *   ID on this realm.
+ * - node_access_test: Grants users view privileges when they have the
+ *   'node test view' permission. Users with this permission receive two group
+ *   IDs for the realm, 8888 and 8889. Access for both realms is identical;
+ *   the second group is added so that the interaction of multiple groups on
+ *   a given grant realm can be tested in NodeAccessPagerTest.
+ * - node_access_all: Provides grants for the user whose user ID matches the
+ *   'node_access_test.no_access_uid' configuration variable. Access control on this
+ *   realm is not provided in this module; instead,
+ *   NodeQueryAlterTest::testNodeQueryAlterOverride() manually writes a node
+ *   access record defining the access control for this realm.
+ *
+ * @see \Drupal\node\Tests\NodeQueryAlterTest::testNodeQueryAlterOverride()
+ * @see \Drupal\node\Tests\NodeAccessPagerTest
+ * @see node_access_test_permission()
+ * @see node_access_test_node_access_records()
  */
 function node_access_test_node_grants($account, $op) {
   $grants = array();
@@ -31,11 +61,23 @@ function node_access_test_node_grants($account, $op) {
 
 /**
  * Implements hook_node_access_records().
+ *
+ * By default, records are written for all nodes. When the
+ * 'node_access_test.private' configuration variable is set to TRUE, records
+ * are only written for nodes with a "private" property set, which causes the
+ * Node module to write the default global view grant for nodes that are not
+ * marked private.
+ *
+ * @see \Drupal\node\Tests\NodeAccessBaseTableTest::setUp()
+ * @see node_access_test_node_grants()
+ * @see node_access_test_permission()
  */
 function node_access_test_node_access_records(EntityInterface $node) {
   $grants = array();
   // For NodeAccessBaseTableTestCase, only set records for private nodes.
   if (!Drupal::state()->get('node_access_test.private') || $node->private) {
+    // Groups 8888 and 8889 for the node_access_test realm both receive a view
+    // grant for all controlled nodes. See node_access_test_node_grants().
     $grants[] = array(
       'realm' => 'node_access_test',
       'gid' => 8888,
@@ -52,7 +94,7 @@ function node_access_test_node_access_records(EntityInterface $node) {
       'grant_delete' => 0,
       'priority' => 0,
     );
-    // For the author realm, the GID is equivalent to a UID, which
+    // For the author realm, the group ID is equivalent to a user ID, which
     // means there are many many groups of just 1 user.
     $grants[] = array(
       'realm' => 'node_access_test_author',
@@ -70,7 +112,14 @@ function node_access_test_node_access_records(EntityInterface $node) {
 /**
  * Implements hook_permission().
  *
- * Sets up permissions for this module.
+ * Provides a 'node test view' permission. By default, all content is
+ * restricted, and users without this permission can only view content they
+ * have authored. When the 'node_access_test.private' configuration variable is
+ * TRUE, only 'private' nodes are restricted, and this permission grants access
+ * to view private nodes.
+ *
+ * @see node_access_test_node_access_records()
+ * @see node_access_test_node_grants()
  */
 function node_access_test_permission() {
   return array('node test view' => array('title' => 'View content'));