It is possible yes to do exactly that you want… the problem is that in fact, you are totally obsessed to execute that action of the way that you want, but to do that, in the wordpress it is in another way, but it is also very simple:
In the page that you made the new layout, that you called index_sub.php or test.php, insert in the top:
<?php
/*
Template Name: New Page
*/
?>
Now, enter in its panel of administration of the wordpress, and create a new page, placing the title that to want, for example, “blog” and if it is using permanlinks the url it will be: http://www.yoursite.com/blog
In this new page doesn’t write anything, just select in the template (to the right) “New Page”, that the new layout that you created was. Then you will notice that that new page that you did can be visualized, getting its objective.
Besides the tsguitar had already said that, but I think you didn’t understand or didn’t know as using.
For more details, it is very important to read at least the basic part of the documentation, the way that the system works and for the templates:
Creating your own Page Templates
