<?php

function shortcode_users_membership() {

  // WP_User_Query arguments
	$args = array(
	  'role'           => 'Author',
	  'orderby'        => 'id',
	  'count_total'    => true,
	  'fields'         => 'all'
	);

	// The User Query
	$user_query = new WP_User_Query( $args );

  	$result = '<ul>';

	// The User Loop
	if ( ! empty( $user_query->results ) ) {
		foreach ( $user_query->results as $user ) {
			$author_info = get_userdata($user->ID);
	  		$result .= '<li>' . $author_info->first_name . ' ' . $author_info->last_name . '</li>';
		}
	  } else {
		  $result .= 'No hay usuarios';
	  }
  	$result .= '</ul>';
	return $result;
}
add_shortcode('users_membership', 'shortcode_users_membership');