.../rest/tests/src/Functional/FileUploadResourceTestBase.php | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php b/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php
index ca3e7ca..ef9b5ce 100644
--- a/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php
@@ -83,11 +83,21 @@
   protected $user;
 
   /**
+   * The entity storage for the 'file' entity type.
+   *
+   * @var \Drupal\Core\Entity\EntityStorageInterface
+   */
+  protected $fileStorage;
+
+  /**
    * {@inheritdoc}
    */
   public function setUp() {
     parent::setUp();
 
+    $this->fileStorage = $this->container->get('entity_type.manager')
+      ->getStorage('file');
+
     // Add a file field.
     $this->fieldStorage = FieldStorageConfig::create([
       'entity_type' => 'entity_test',
@@ -172,6 +182,7 @@ public function testPostFileUpload() {
 
     // Check the actual file data.
     $this->assertSame($this->testFileData, file_get_contents('public://foobar/example_0.txt'));
+    $this->assertTrue($this->fileStorage->loadUnchanged(1)->isTemporary());
 
     // Verify that we can create an entity that references the uploaded file.
     $entity_test_post_url = Url::fromRoute('rest.entity.entity_test.POST')
@@ -183,6 +194,7 @@ public function testPostFileUpload() {
     $request_options[RequestOptions::BODY] = $this->serializer->encode($this->getNormalizedPostEntity(), static::$format);
     $response = $this->request('POST', $entity_test_post_url, $request_options);
     $this->assertResourceResponse(201, FALSE, $response);
+    $this->assertTrue($this->fileStorage->loadUnchanged(1)->isPermanent());
     // @todo Remove this early return in https://www.drupal.org/project/drupal/issues/2935738.
     if (static::$format === 'hal_json') {
       return;