Way to test ansible jinja templates (.j2) independently from playbooks

hosts

#add local to existing ansible hosts, to get variable from your hosts
[local]
127.0.0.1

[app]
test1 app_name=app1
test2 app_name=app2

test.j2

{vm_endpoints, [{% for host in groups['app'] %} "{{ hostvars[host]['app_name']}}" {% if not loop.last %}, {% endif %}{% endfor %}]}.

test.sh

#!/bin/bash
#example invocation:
ansible-playbook -i hosts --check --diff --connection=local test.yml

test.yml

---
- hosts: 127.0.0.1
  connection: local
  tasks:
  - name: Test jinja2template
    template: src=test.j2 dest=test.conf