Isn't Kali basend on testing and not on sid/unstable and one packages arrive in testing are also included in Kali again?

Kali is indeed based on Debian testing. You can check the status of hplip in Debian on this page: https://tracker.debian.org/pkg/hplip

There are 2 bugs that prevent this package from re-entering Debian testing: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1075069 and https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1085142. As long as these issues are not resolved in Debian, the package won't enter Debian testing, hence won't be in Kali.

This report has been filed against an old version of Kali. We will be closing this ticket due to inactivity.

Please could you see if you are able to replicate this issue with the latest version of Kali Linux (https://www.kali.org/get-kali/)?

If you are still facing the same problem, feel free to re-open the ticket. If you choose to do this, could you provide more information to the issue you are facing, and also give information about your setup?
For more information, please read: https://www.kali.org/docs/community/submitting-issues-kali-bug-tracker/