ansible/test/integration/targets/handlers/test_handlers_include.yml

- name: verify that play can include handler
  hosts: testhost
  tasks:
    - debug: msg="main task"
      changed_when: True
      notify: test handler
      tags: ['playbook_include_handlers']
  handlers:
    - include: handlers.yml

- name: verify that role can include handler
  hosts: testhost
  roles:
    - { role: test_handlers_include, tags: ['role_include_handlers'] }