Testing page.

For testing code snippets.

<?php
function restrict_page_to_user() {
    // Replace with the slug or ID of your page
    $restricted_page_slug = '/testing-page';
    // $restricted_user_id = 1; // Replace with the user ID of the user who should have access

    if (is_page($restricted_page_slug) && !is_user_logged_in()) {
        // Redirect non-logged-in users to the login page
        wp_redirect(wp_login_url(get_permalink()));
        exit;
    } elseif (is_page($restricted_page_slug)) {
        $current_user = wp_get_current_user();
        //if ($current_user->ID !== $restricted_user_id) {
        //    // Redirect other logged-in users to a 403 Forbidden page or homepage
        //    wp_redirect(home_url('/403-forbidden')); // You can create a custom 403 page or use the homepage
        //    exit;
        //}
        echo 'The current logged in user ID is: '.get_current_user_id();
    }
}
add_action('template_redirect', 'restrict_page_to_user');
?>