Specifying template does not work

Trying to use:

[ic_add_posts post_type='testimonial' showposts='1' order='random' template='testimonial.php']

But testimonial.php (in my theme directory) is NOT being used as the template. Instead the default template “posts_loop_template.php” is being used. If I copy posts_loop_template.php to my theme directory, and make changes to that file, they show up instead of the customizations in testimonial.php, which is right beside “posts_loop_template.php” in my theme directory.

Any thoughts on why it isnt working?

https://wordpress.org/plugins/posts-in-page/