- name: test become
      shell: "whoami"
      register: shell_result
      become_user: jenkins

    - debug:
        msg: "{{shell_result.stdout}}"

TASK [debug] ***********************************************************************************************************************************
ok: [test-vm] => {
    "msg": "george"
}

 fatal: [test-vm]: UNREACHABLE! => {"changed": false, "msg": "Authentication or permission failure. In some cases, you may ha
ve been able to authenticate and did not have permissions on the target directory. Consider changing the remote tmp path in ansible.cfg to a pat
h rooted in \"/tmp\". Failed command was: ( umask 77 && mkdir -p \"` echo /var/tmp/ansible-tmp-1595412196.294242-18928345142486 `\" && echo ansi
ble-tmp-1595412196.294242-18928345142486=\"` echo /var/tmp/ansible-tmp-1595412196.294242-18928345142486 `\" ), exited with result 1", "unreachab
le": true}

 FAILED! => {"msg": "Failed to set permissions on the temporary files Ansible needs to create when becoming
 an unprivileged user (rc: 1, err: chown: changing ownership of '/var/tmp/ansible-tmp-1595412013.979855-144795728313297/': Operation not permitt
ed\nchown: changing ownership of '/var/tmp/ansible-tmp-1595412013.979855-144795728313297/AnsiballZ_command.py': Operation not permitted\n}). For
 information on working around this, see https://docs.ansible.com/ansible/become.html#becoming-an-unprivileged-user"}