Widgets: Add tests for retrieve_widgets().

Helps with maintaining back compat when making changes in the future.

See #39693.


Built from https://develop.svn.wordpress.org/trunk@41266


git-svn-id: http://core.svn.wordpress.org/trunk@41106 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9-alpha-41265';
+$wp_version = '4.9-alpha-41266';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.