ansible/test/integration/targets/set_fact/set_fact_empty_str_key.yml

- name: Test set_fact for empty string as a key
  hosts: testhost
  gather_facts: no
  vars:
    value: 1
  tasks:
    - name: Define fact with key as an empty string
      set_fact:
        foo:
          "": "bar{{ value }}"

    - name: Verify the parsed value of the key
      assert:
        that:
          - foo == {"":"bar1"}