WordPress allows you to preview posts, pages and other CPTs, even you can preview themes but WordPress doesn’t provides you any feature for previewing widgets. This tutorial explains how you can easily enable preview mode for selected widgets so that you can preview new widgets before to make them publicly visible on your website.
So first install and activate the new WordPress plugin called WP Widget Preview. After activation the plugin automatically adds a preview mode checkbox option on all of your site’s widgets.
Now visit Dashboard -> Appearance -> Widgets page, drag the widget to sidebar and simply tick Preview Mode checkbox. This make checkbox option enables the preview mode for that particular widgets and the widget comes only visible to site administrators.