Issue #1824926 by vijaycs85: Convert image_module_test_file_download() variable to CMI system.

core/modules/image/lib/Drupal/image/Tests/ImageStylesPathAndUrlTest.php

@@ -106,7 +106,7 @@ function _testImageStyleUrlAndPath($scheme, $clean_url = TRUE) {
     $original_uri = file_unmanaged_copy($file->uri, $scheme . '://', FILE_EXISTS_RENAME);
     // Let the image_module_test module know about this file, so it can claim
     // ownership in hook_file_download().
-    variable_set('image_module_test_file_download', $original_uri);
+    state()->set('image.test_file_download', $original_uri);
     $this->assertNotIdentical(FALSE, $original_uri, 'Created the generated image file.');
 
     // Get the URL of a file that has not been generated and try to create it.

core/modules/image/tests/image_module_test.module

@@ -6,7 +6,8 @@
  */
 
 function image_module_test_file_download($uri) {
-  if (variable_get('image_module_test_file_download', FALSE) == $uri) {
+  $default_uri = state()->get('image.test_file_download') ?: FALSE;
+  if ($default_uri == $uri) {
     return array('X-Image-Owned-By' => 'image_module_test');
   }
 }