Testing PHP method that depends on another method

Unsure of the best way to unit test this:

<?php

class Test
{
    public static function random(){
        return rand(0,9);
    }

    public static function nonDuplicateRandom($dupes){
        $rand = self::random();
        while(in_array($rand, $dupes)){
            $rand = self::random();
        }
        return $rand;
    }
}

echo Test::nonDuplicateRandom(array(0,1,2,3,4,5));

Should I modify nonDuplicateRandom so it can be passed a $rand value to test against or is there a better way?