WordPress functions.php

/*----------------------------------------------------
 投稿をランダムに1件取得
----------------------------------------------------*/
if ( !function_exists( 'add_category_color_field' ) ){
    function get_the_post_rand( $atts ){
        extract( shortcode_atts( array(
           'post_type'      => 'post',
           'posts_per_page' => 1, //取得件数
           'not_in'         => '',
        ), $atts) );

        $args = array(
            'post_type'      => $post_type,
            'posts_per_page' => $posts_per_page,
            'orderby'        => 'rand',      // ランダム指定
            'post__not_in'   => array($not_in), // 自記事を除外したりする場合に使用
        );
        
        $the_query = new WP_Query( $args );

        if ( $the_query->have_posts() ) {

            echo '<div>';

            while ( $the_query->have_posts() ) {
                $the_query->the_post();
                echo '<article>';
                echo '    <div>';
                echo '        <h3><a href="'.get_the_permalink().'" title="'.get_the_title().'">'.get_the_title().'</a></h3>';
                echo '    </div>';
                echo '</article>';
            }

            echo '</div>';
        }
        wp_reset_postdata();
    }
    add_shortcode('post_rand', 'get_the_post_rand');
}

<?php echo do_shortcode('[post_rand]'); ?>

<?php echo do_shortcode('[post_rand post_type=news posts_per_page=2]'); ?>