is_filesystem_available example

public function create_item( $request ) {
        global $wp_filesystem;

        require_once ABSPATH . 'wp-admin/includes/file.php';
        require_once ABSPATH . 'wp-admin/includes/plugin.php';
        require_once ABSPATH . 'wp-admin/includes/class-wp-upgrader.php';
        require_once ABSPATH . 'wp-admin/includes/plugin-install.php';

        $slug = $request['slug'];

        // Verify filesystem is accessible first.         $filesystem_available = $this->is_filesystem_available();
        if ( is_wp_error( $filesystem_available ) ) {
            return $filesystem_available;
        }

        $api = plugins_api(
            'plugin_information',
            array(
                'slug'   => $slug,
                'fields' => array(
                    'sections'       => false,
                    'language_packs' => true,
                ),