How can I test jinja2 templates in ansible?

Question

Sometimes I need to test some jinja2 templates that I use in my ansible roles. What is the simplest way for doing this?

For example, I have a template (test.j2):

{% if users is defined and users %}
{% for user in users %}{{ user }}
{% endfor %}
{% endif %}

and vars (in group_vars/all):

---
users:
  - Mike
  - Smith
  - Klara
  - Alex

Answer 1

At this time exists 4 different variants:

1_Online (using https://cryptic-cliffs-32040.herokuapp.com/)
Based on jinja2-live-parser code.

2_Interactive (using python and library jinja2, PyYaml)

import yaml
from jinja2 import Template
>>> template = Template("""
... {% if users is defined and users %}
... {% for user in users %}{{ user }}
... {% endfor %}
... {% endif %}
... """)
>>> values = yaml.load("""
... ---
... users:
...   - Mike
...   - Smith
...   - Klara
...   - Alex
... """)
>>> print "{}".format(template.render(values))


Mike
Smith
Klara
Alex

3_Ansible (using --check)
Create test playbook jinja2test.yml:

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

and run it:

ansible-playbook jinja2test.yml --check --diff --connection=local

sample output:

PLAY [127.0.0.1] **************************************************************

GATHERING FACTS ***************************************************************

ok: [127.0.0.1]

TASK: [Test jinja2template] ***************************************************
--- before: test.conf
+++ after: /Users/user/ansible/test.j2
@@ -0,0 +1,4 @@
+Mike
+Smith
+Klara
+Alex

changed: [127.0.0.1]

PLAY RECAP ********************************************************************
127.0.0.1                  : ok=2    changed=1    unreachable=0    failed=0

4_Ansible (using -m template) thanks for @artburkart

Make a file called test.txt.j2

{% if users is defined and users %}
{% for user in users %}
{{ user }}
{% endfor %}
{% endif %}

Call ansible like so:

ansible all -i "localhost," -c local -m template -a "src=test.txt.j2 dest=./test.txt" --extra-vars='{"users": ["Mike", "Smith", "Klara", "Alex"]}'

It will output a file called test.txt in the current directory, which will contain the output of the evaluated test.txt.j2 template.

I understand this doesn't directly use a vars file, but I think it's the simplest way to test a template without using any external dependencies. Also, I believe there are some differences between what the jinja2 library provides and what ansible provides, so using ansible directly circumvents any discrepancies. When the JSON that is fed to --extra-vars satisfies your needs, you can convert it to YAML and be on your way.