Issue #1963764 by widukind, pwieck: Convert theme_views_view_mapping_test() to Twig.

core/modules/views/templates/views-view-mapping-test.html.twig

+{#
+/**
+ * @file
+ * Default theme implementation for testing the mapping row style.
+ *
+ * Available variables:
+ * - element: The view content.
+ *
+ * @see template_preprocess_views_view_mapping_test()
+ *
+ * @ingroup themeable
+ */
+#}
+{{ element }}

core/modules/views/tests/modules/views_test_data/views_test_data.module

@@ -67,7 +67,15 @@ function views_test_data_preprocess_views_view_table(&$variables) {
 }
 
 /**
- * Implements hook_preprocess_HOOK() for theme_views_view_mapping_test().
+ * Prepares variables for the mapping row style test templates.
+ *
+ * Default template: views-view-mapping-test.html.twig.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - rows: A list of view rows.
+ *   - options: Various view options, including the row style mapping.
+ *   - view: The view object.
  */
 function template_preprocess_views_view_mapping_test(&$variables) {
   $variables['element'] = array();
@@ -114,10 +122,3 @@ function template_preprocess_views_view_mapping_test(&$variables) {
     }
   }
 }
-
-/**
- * Returns HTML for the Mapping Test style.
- */
-function theme_views_view_mapping_test($variables) {
-  return drupal_render($variables['element']);
-}