.../Drupal/system/Tests/Entity/EntityCacheTagsTestBase.php   |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityCacheTagsTestBase.php b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityCacheTagsTestBase.php
index ed082d8..d426390 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityCacheTagsTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityCacheTagsTestBase.php
@@ -97,7 +97,7 @@ public function setUp() {
   }
 
   /**
-   * Generates the standardized test info.
+   * Generates standardized entity cache tags test info.
    *
    * @param string $entity_type_label
    *   The label of the entity type whose cache tags to test.
@@ -119,6 +119,10 @@ protected static function generateStandardizedInfo($entity_type_label, $group) {
   /**
    * Creates the entity to be tested.
    *
+   * This is a static method to guarantee that subclasses that implement it
+   * don't set additional properties on the object: it ensures a clear, strict
+   * contract.
+   *
    * @return \Drupal\Core\Entity\EntityInterface
    *   The entity to be tested.
    */
@@ -134,6 +138,10 @@ protected static function createEntity() {
   /**
    * Creates a referencing and a non-referencing entity for testing purposes.
    *
+   * This is a static method to guarantee that subclasses that override it
+   * don't set additional properties on the object: it ensures a clear, strict
+   * contract.
+   *
    * @param \Drupal\Core\Entity\EntityInterface $referenced_entity
    *  The entity that the referencing entity should reference.
    *