0-inventory - hosts.ini

[k8s_gpu_nodes]
host1
host2
[k8s_cpu_nodes]
host3
host4

1- roles - test - tasks - main.yml

---
- name: Check everything is ok
  vars:
    gpu_count: "{{ groups['k8s_gpu_nodes'] | length }}"
    cpu_count: "{{ groups['k8s_cpu_nodes'] | length }}"
  assert:
    that:
      - gpu_count | int > 0
      - cpu_count | int > 0
    msg: "Assure k8s_nodes are not empty"

2-playbook.yml

---
- name: Check nodes in groups
  hosts: localhost
  gather_facts: false

  roles:
    - role: test

3.result

$ ansible-playbook -i inventories/hosts.ini playbook.yml 

PLAY [Check nodes in groups] ****************************************************************************************************************************************************************************

TASK [test : Check everything is ok] ********************************************************************************************************************************************************************
ok: [localhost] => {
    "changed": false,
    "msg": "All assertions passed"
}

PLAY RECAP **********************************************************************************************************************************************************************************************
localhost                  : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   

I checked out this and ran as is and getting error

ERROR! the role 'test' was not found in /home/dtlu/code/github/sb8884/692abf1de75e44fa607fa052f09360e2/roles:/home/dtlu/.ansible/roles:/usr/share/ansible/roles:/etc/ansible/roles:/home/dtlu/code/github/sb8884/692abf1de75e44fa607fa052f09360e2

The error appears to be in '/home/dtlu/code/github/sb8884/692abf1de75e44fa607fa052f09360e2/2-playbook.yml': line 7, column 7, but may
be elsewhere in the file depending on the exact syntax problem.

The offending line appears to be:

  roles:
    - role: test
      ^ here

Then I created a directory as role_test/tasks and added main.yaml. now it works.