- hosts: localhost
  gather_facts: no
  tasks:
    - set_fact:
        test: 123
      delegate_to: "{{ item }}"
      delegate_facts: true
      when: test is not defined
      loop: "{{ groups['all'] | difference(['localhost']) }}"

    - name: ensure we didnt create it on current host
      assert:
        that:
          - test is undefined

    - name: ensure facts get created
      assert:
        that:
          - "'test' in hostvars[item]"
          - hostvars[item]['test'] == 123
      loop: "{{ groups['all'] | difference(['localhost']) }}"