Issue #1898456 by joelpittet: Common_test().module - Convert theme_ functions to Twig.

core/modules/system/tests/modules/common_test/common_test.module

@@ -249,17 +249,11 @@ function common_test_theme() {
   return array(
     'common_test_foo' => array(
       'variables' => array('foo' => 'foo', 'bar' => 'bar'),
+      'template' => 'common-test-foo',
     ),
   );
 }
 
-/**
- * Provides a theme function for drupal_render().
- */
-function theme_common_test_foo($variables) {
-  return $variables['foo'] . $variables['bar'];
-}
-
 /**
  * Implements hook_library_info_alter().
  */

core/modules/system/tests/modules/common_test/templates/common-test-foo.html.twig

+{#
+/**
+ * @file
+ * Default theme implementation for the common test foo.
+ *
+ * Available variables:
+ * - foo: foo.
+ * - bar: bar.
+ *
+ * @see template_preprocess()
+ *
+ * @ingroup themeable
+ */
+#}
+{{ foo }}{{ bar -}}