.../EntityResource/EntityResourceTestBase.php      | 83 +++++++++++++---------
 1 file changed, 50 insertions(+), 33 deletions(-)

diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index c8240d2..5ef55ee 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -7,6 +7,7 @@
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Cache\CacheableResponseInterface;
 use Drupal\Core\Config\Entity\ConfigEntityInterface;
+use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\FieldableEntityInterface;
 use Drupal\Core\Field\Plugin\Field\FieldType\BooleanItem;
 use Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItem;
@@ -1025,39 +1026,9 @@ public function testPatch() {
 
 
     // DX: 403 when sending PATCH request with updated read-only fields.
-    // Clone the entity, modifies all PATCH-protected fields. Then performs a
-    $modified_entity = clone $this->entity;
-    $original_values = [];
-    foreach (static::$patchProtectedFieldNames as $field_name) {
-      $field = $modified_entity->get($field_name);
-      $original_values[$field_name] = $field->getValue();
-      switch ($field->getItemDefinition()->getClass()) {
-        case EntityReferenceItem::class:
-          // EntityReferenceItem::generateSampleValue() picks one of the last 50
-          // entities of the supported type & bundle. We don't care if the value
-          // is valid, we only care that it's different.
-          $field->setValue(['target_id' => 99999]);
-          break;
-        case BooleanItem::class:
-          // BooleanItem::generateSampleValue() picks either 0 or 1. So a 50%
-          // chance of not picking a different value.
-          $field->value = ((int) $field->value) === 1 ? '0' : '1';
-          break;
-        case PathItem::class:
-          // PathItem::generateSampleValue() doesn't set a PID, which causes
-          // PathItem::postSave() to fail. Keep the PID (and other properties),
-          // just modify the alias.
-          $value = $field->getValue();
-          $value['alias'] = str_replace(' ', '-', strtolower((new Random())->sentences(3)));
-          $field->setValue($value);
-          break;
-        default:
-          $field->generateSampleItems();
-          break;
-      }
-    }
-    // Send PATCH request by serializing the cloned entity, assert the error
-    // response, change the cloned entity field that caused the error response
+    list($modified_entity, $original_values) = static::getModifiedEntityForPatchTesting($this->entity);
+    // Send PATCH request by serializing the modified entity, assert the error
+    // response, change the modified entity field that caused the error response
     // back to its original value, repeat.
     for ($i = 0; $i < count(static::$patchProtectedFieldNames); $i++) {
       $patch_protected_field_name = static::$patchProtectedFieldNames[$i];
@@ -1293,6 +1264,52 @@ protected function getEntityResourcePostUrl() {
   }
 
   /**
+   * Clones the given entity and modifies all PATCH-protected fields.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity being tested and to modify.
+   *
+   * @return array
+   *   Contains two items:
+   *   1. The modified entity object.
+   *   2. The original field values, keyed by field name.
+   */
+  protected static function getModifiedEntityForPatchTesting(EntityInterface $entity) {
+    $modified_entity = clone $entity;
+    $original_values = [];
+    foreach (static::$patchProtectedFieldNames as $field_name) {
+      $field = $modified_entity->get($field_name);
+      $original_values[$field_name] = $field->getValue();
+      switch ($field->getItemDefinition()->getClass()) {
+        case EntityReferenceItem::class:
+          // EntityReferenceItem::generateSampleValue() picks one of the last 50
+          // entities of the supported type & bundle. We don't care if the value
+          // is valid, we only care that it's different.
+          $field->setValue(['target_id' => 99999]);
+          break;
+        case BooleanItem::class:
+          // BooleanItem::generateSampleValue() picks either 0 or 1. So a 50%
+          // chance of not picking a different value.
+          $field->value = ((int) $field->value) === 1 ? '0' : '1';
+          break;
+        case PathItem::class:
+          // PathItem::generateSampleValue() doesn't set a PID, which causes
+          // PathItem::postSave() to fail. Keep the PID (and other properties),
+          // just modify the alias.
+          $value = $field->getValue();
+          $value['alias'] = str_replace(' ', '-', strtolower((new Random())->sentences(3)));
+          $field->setValue($value);
+          break;
+        default:
+          $field->generateSampleItems();
+          break;
+      }
+    }
+
+    return [$modified_entity, $original_values];
+  }
+
+  /**
    * Makes the given entity normalization invalid.
    *
    * @param array $normalization