Molecule: define host_vars or group_vars in provisioner/inventory that are really used by Molecule´s platform

molecule.yml

# Roles which require host/groups to have certain variables set 
# see (scroll down!) https://molecule.readthedocs.io/en/latest/configuration.html#provisioner & https://github.com/ansible/molecule/issues/1037
# like:
provisioner:
  name: ansible
  ...
  inventory:
    host_vars:
      docker-debian-stretch:
        gitlab_domain: "localhost"
        
# Molecule uses the name of the Platform to create an inventory host name
# you have to do nothing, if you chooce the same name there (& host_vars in provisioner) like this:
platforms:
  - name: docker-debian-stretch
    ... 

# if you use group_vars under inventory, you have to define groups also under Platforms:
# see https://molecule.readthedocs.io/en/latest/configuration.html#platforms
platforms:
  - name: docker-debian-stretch
    groups:
      - other-name-then-docker-debian-stretch
      
# but now you can´t re-use the nice platform name - so just stay with host_vars :)