Automatically set featured image to all posts in a post type

gistfile1.txt

add_action('init','set_post_thumbnails');
function set_post_thumbnails() {

    // Query args
    $args = array(
		'post_type' => 'testimonials',
		'posts_per_page' => '-1'
    );
    // Run query
    $query = new WP_Query( $args );

    // Open query loop
    if ( $query->have_posts() ) : while ( $query->have_posts() ) : $query->the_post();

  		 set_post_thumbnail( get_the_ID(), '2733' );

    // Close query loop
    endwhile; endif;
    wp_reset_postdata();

}