I have added a user like this:
$ adduser --system --home /no/home --no-create-home --group --disabled-password --disabled-login testuser
Ad
sudo
permissions are about the user/group you are changing from not the user you are changing to.
So are those permission lines are letting the testuser
user and the testgroup
group run any command (as anyone) without a password.
You need to give permission to the user running the script to run commands as the testuser
user for what you want.
Assuming that's what you meant to allow that is.