Issue #3042869 by claudiu.cristea, Lendude: Convert UpdateDeleteFileIfStaleTest into a Kernel test

(cherry picked from commit bdd4ddb9)

core/modules/update/tests/src/Functional/UpdateDeleteFileIfStaleTest.php → core/modules/update/tests/src/Kernel/UpdateDeleteFileIfStaleTest.php

 <?php
 
-namespace Drupal\Tests\update\Functional;
+namespace Drupal\Tests\update\Kernel;
+
+use Drupal\KernelTests\KernelTestBase;
 
 /**
  * Tests the update_delete_file_if_stale() function.
  *
  * @group update
  */
-class UpdateDeleteFileIfStaleTest extends UpdateTestBase {
-
-  /**
-   * Modules to enable.
-   *
-   * @var array
-   */
-  public static $modules = ['update'];
+class UpdateDeleteFileIfStaleTest extends KernelTestBase {
 
   /**
    * {@inheritdoc}
    */
-  protected function setUp() {
-    parent::setUp();
-  }
+  protected static $modules = [
+    'system',
+    'update',
+  ];
 
   /**
    * Tests the deletion of stale files.
    */
   public function testUpdateDeleteFileIfStale() {
-    $file_name = \Drupal::service('file_system')->saveData($this->randomMachineName(), 'public://');
+    $file_system = $this->container->get('file_system');
+
+    $file_name = $file_system->saveData($this->randomMachineName(), 'public://');
     $this->assertNotNull($file_name);
 
     // During testing the file change and the stale checking occurs in the same
     // request, so the beginning of request will be before the file changes and
-    // REQUEST_TIME - $filectime is negative. Set the maximum age to a number
-    // even smaller than that.
+    // REQUEST_TIME - $filectime is negative or zero. Set the maximum age to a
+    // number even smaller than that.
     $this->config('system.file')
       ->set('temporary_maximum_age', -100000)
       ->save();
 
-    $file_path = \Drupal::service('file_system')->realpath($file_name);
+    $file_path = $file_system->realpath($file_name);
     update_delete_file_if_stale($file_path);
 
-    $this->assertFalse(is_file($file_path));
+    $this->assertFileNotExists($file_path);
   }
 
 }