ansible/test/integration/test_var_precedence.yml

---
- hosts: testhost
  vars:
  - vars_var: "vars_var"
  - param_var: "BAD!"
  - vars_files_var: "BAD!"
  vars_files:
  - vars/test_var_precedence.yml
  roles:
  - { role: test_var_precedence, param_var: "param_var" }
  tasks:
  - name: register a result
    command: echo 'BAD!'
    register: registered_var
  - name: use set_fact to override the registered_var
    set_fact: registered_var="this is from set_fact"
  - debug: var=extra_var
  - debug: var=vars_var
  - debug: var=vars_files_var
  - debug: var=vars_files_var_role
  - debug: var=registered_var
  - assert:
      that:
        - 'extra_var == "extra_var"'
        - 'vars_var == "vars_var"'
        - 'vars_files_var == "vars_files_var"'
        - 'vars_files_var_role == "vars_files_var_role3"'
        - 'registered_var == "this is from set_fact"'

- hosts: inven_overridehosts
  vars_files:
  - "{{ var_dir }}/test_var_precedence.yml"
  roles:
  - role: test_var_precedence_inven_override
    foo: bar