/** Category Widget Filter || Exclude Category by Slug */
function filter_category_widget( $cat_args, $instance ) {
	$list_slug = array( 'apps', 'review', 'world', 'business', 'category-test-slug' ); /* Category Slug */

	foreach( $list_slug as $slug ) {
		$cat_args['exclude'][] = get_category_by_slug( $slug )->term_id;
	}

	return $cat_args;
}
add_filter( 'widget_categories_args', 'filter_category_widget', null, 2 );