Just in case anybody else has this issue when they try to use amp config with CiviBuild. It is probably not entirely clear that you first need to create the user that you are inputting into the Enter dsn>
You first need to create a user in mysql with sufficent privileges. Remember, one does not log in as root anymore! Use 'sudo su' and then run your ...
I found the answer: I was using a backup: the CiviCRM unit test framework uses files and services not found without doing a git clone (or buildkit equivalent). The folders you need from a git clone are Tests and Tools.
Leaving this here in case it assists someone who encounters the same problem.