Test Flask render_template() context

Question

I have a Flask route that looks like this:

@app.route('/')                                                                  def home():                                                                                                                       return render_template(                                                              'home.html',                                                                     greeting:"hello"                                            )                                                                            

How do I test that the 'home.html' template was rendered, and that the render_template() context defined the greeting variable with a particular value?

These should be (and probably are) pretty easy to test, but I'm really not sure how to do this with Flask and unittest.

Answer 1

You can use the assert_template_used method of TestCase provided by flask-testing.

from flask.ext.testing import TestCase  class MyTest(TestCase):      def create_app(self):         return myflaskapp      def test_greeting(self):         self.app.get('/')         self.assert_template_used('hello.html')         self.assert_context("greeting", "hello") 

The method create_app must provide your flask app.

Answer 2

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