Test Flask render_template() context

Question

I have a Flask route that looks like this:

@app.route(\'/\')                                                                 
def home():                             


        

Answer 1

Flask official documentation suggests that you use the template_rendered signal (available since version 0.6) for unit-testing your templates and the variables used to render it.

For example, here is a helper context manager that can be used in a unittest to determine which templates were rendered and what variables were passed to the template:

from flask import template_rendered
from contextlib import contextmanager

@contextmanager
def captured_templates(app):
    recorded = []
    def record(sender, template, context, **extra):
        recorded.append((template, context))
    template_rendered.connect(record, app)
    try:
        yield recorded
    finally:
        template_rendered.disconnect(record, app)

This can now easily be paired with a test client:

with captured_templates(app) as templates:
    rv = app.test_client().get('/')
    assert rv.status_code == 200
    assert len(templates) == 1
    template, context = templates[0]
    assert template.name == 'index.html'
    assert len(context['items']) == 10