ansible/test/integration/targets/builtin_vars_prompt/unsupported.yml

- name: Test vars_prompt unsupported key
  hosts: testhost
  become: no
  gather_facts: no
  vars_prompt:
    - name: input
      prompt: prompting for variable
      # Unsupported key for vars_prompt
      when: foo is defined

  tasks:
    - name:
      assert:
        that:
          - input is not defined

    - debug:
        var: input