Using wordpress functions outside wordpress version 4.4

Question

I am trying to use some wordpress function in a script located in the wordpress root directory, just that some of the wordpress functions work others don't: get_users function works well but wp_delete_user doesn't. What am I missing? PLugin is out of discussion.

require($_SERVER['DOCUMENT_ROOT']."/wp-blog-header.php");
global $wpdb;
$args = array(
    'role' => 'test_taker'
);
$users = get_users( $args ); // This works
//var_dump($users);
foreach ($users as $user) {
    //var_dump($user->ID);
    wp_delete_user( $user->ID ); // This doesn't work
}

Answer 1

Managed to find the solution. When you get undefined function, that means you need to copy the function into the external file. For example in my case wp_delete_user needed to copy it from here https://developer.wordpress.org/reference/functions/wp_delete_user/