get categories fixed in dropdown

I’m trying to build an mobile app for my site, i missing to access categories fixed in dropdown directly from database or from an php page:
1) i can’t biuld querry to get it
2) i tried to run this script in public_html but it’s return
Fatal error: Call to undefined function get_categories() in /mnt/env/****/development/public_html/test.php on line 9
`<?php

include “wp-includes/category-template.php”;

$args = array(
‘hide_empty’ => 0,
‘pad_counts’ => true
);
$categories = get_categories( $args );
foreach($categories as $category) {

if($category->count == 0) {
echo $category->name.”<br />”;
} else {
// do nothing
}

}
?>`