---
- hosts: 127.0.0.1
user: root
tasks:
- name: Remove myuser from mygoup
become: true
command: "gpasswd -d myuser mygroup"
register: command_result
changed_when: "not 'is not a member of' in command_result.stderr"
failed_when: "'does not exist in /etc/group' in command_result.stderr"