exclude testimonial query from index post

<?php
//condition : যদি এই query, category testimonial না হয়, এবং এটি main query হয়, তাহলে testimonial category exclude কর,
//(-5 is testimonial category id) (! means is not)

function exclude_testimonials( $query ) {
    if( !$query->is_category('testimonials') && $query->is_main_query()) {
        $query->set('cat', '-5');
    }
}
add_action('pre_get_posts', 'exclude_testimonials');
?>