Shuffle a batch of posts in PHP instead of using orderby => rand with WP_Query

php-shuffle.php

<?php
$testimonial = false;
$testimonials_query = new WP_Query( array( 'fields' => 'ids', 'posts_per_page' => 20 ) );

if ( ! empty ( $testimonials_query->posts ) ) {
    $testimonials = $testimonials_query->posts;
    shuffle( $testimonials );

    $testimonial_id = array_shift( $testimonials );
    $testimonial = get_post( $testimonial_id );
}