A test for how jinja2 handles nested blocks defined in inheriting templates.

a.html

{% block outer %}
{% endblock %}

b.html

{% extends 'a.html' %}
{% block outer %}
  {% block inner %}
    Hi.
  {% endblock %}
{% endblock %}

render.py

import sys                                   
from jinja2 import Environment
from jinja2.loaders import FileSystemLoader


env = Environment(loader=FileSystemLoader('.'))
print env.get_template(sys.argv[1]).render()

python render.py b.html gives

Hi.