only in patch2:
unchanged:
--- a/core/modules/rest/src/Tests/UpdateTest.php
+++ b/core/modules/rest/src/Tests/UpdateTest.php
@@ -52,6 +52,8 @@ public function testPatchUpdate() {
     $patch_entity = entity_create($entity_type, $patch_values);
     // We don't want to overwrite the UUID.
     unset($patch_entity->uuid);
+    // We don't want to overwrite the changed time.
+    unset($patch_entity->changed);
     $serialized = $serializer->serialize($patch_entity, $this->defaultFormat);
 
     // Update the entity over the REST API.
only in patch2:
unchanged:
--- a/core/modules/serialization/src/Tests/EntitySerializationTest.php
+++ b/core/modules/serialization/src/Tests/EntitySerializationTest.php
@@ -59,6 +59,7 @@ protected function setUp() {
     );
     $this->entity = entity_create('entity_test_mulrev', $this->values);
     $this->entity->save();
+    $this->values['changed'] = $this->entity->getChangedTime();
 
     $this->serializer = $this->container->get('serializer');
 
@@ -88,6 +89,9 @@ public function testNormalize() {
       'user_id' => array(
         array('target_id' => $this->values['user_id']),
       ),
+      'changed' => array(
+        array('value' => $this->values['changed']),
+      ),
       'revision_id' => array(
         array('value' => 1),
       ),
@@ -136,6 +140,7 @@ public function testSerialize() {
       'name' => '<name><value>' . $this->values['name'] . '</value></name>',
       'type' => '<type><value>entity_test_mulrev</value></type>',
       'user_id' => '<user_id><target_id>' . $this->values['user_id'] . '</target_id></user_id>',
+      'changed' => '<changed><value>' . $this->values['changed'] . '</value></changed>',
       'revision_id' => '<revision_id><value>' . $this->entity->getRevisionId() . '</value></revision_id>',
       'field_test_text' => '<field_test_text><value>' . $this->values['field_test_text']['value'] . '</value><format>' . $this->values['field_test_text']['format'] . '</format></field_test_text>',
     );