- hosts: testhost,testhost2
  gather_facts: no
  tasks:
    - set_fact:
        module_to_run: 'debug'
      when: inventory_hostname == 'testhost'

    - set_fact:
        module_to_run: 'ping'
      when: inventory_hostname == 'testhost2'

    - action:
        module: '{{ module_to_run }}'
      register: out

    - assert:
        that:
          - "'msg' in out"
          - "'ping' not in out"
      when: inventory_hostname == 'testhost'

    - assert:
        that:
          - "'ping' in out"
          - "'msg' not in out"
      when: inventory_hostname == 'testhost2'