Conditional WordPress tag to detect page templates when the page is used to display posts, not page content

is_custom_page_template.php

<?php
/**
 * is_custom_page_template()
 *
 * This is used to test the current page template when the page template in question is used to display
 * posts (post archives), not regular page content. The default conditional tag is_page_template() fails
 * in this situation, so we're using this in-house function instead.
 *
 *
 * @since 0.1.0
 *
 * @global $wp_query WordPress query object.
 * @param string $template Page template file name (e.g. page-front.php)
 * @return bool Returns false if page template was not found.
 */
function is_custom_page_template( $template = '' ) {
	global $wp_query;
	 
	$page_id = $wp_query->get_queried_object_id();
	 
	if ( $template == get_post_meta( $page_id, '_wp_page_template', true ) )
		return true;
	else
		return false;
}