Masahiro NAKASHIMA

If this plug-in is enabled, and there is a file on the same theme level as the static page URL level, then that theme file will automatically be loaded as the template file.
Example 
For the static page URL: “http://example.com/foo/bar/” 
Theme directory: “/wp-content/themes/mytheme/foo/bar/index.php” 
will be loaded as the template file if it exists.
*If enabled themes have a parent-child relationship, then the file for the child theme will be loaded with precedence.

Auto Load Page Template

If this plug-in is enabled, and there is a file on the same theme level as the static page URL level, then that theme file will automatically be loade …

The theme can be changed and displayed to only logged in users.
The visitors of the website see your old theme while you are testing the new one.
Only the administrator of the WordPress site sees the new theme that can now be tested safely.
You can also use this plugin instead of “Theme Test Drive” plugin.

WP Theme Test

I have xdebug installed. There are two big Notices.

Threw two big PHP notices

The theme can be changed and displayed to only logged in users.

Auto Load Page Template vs WP Theme Test