Proper way to test Django signals

Question

I'm trying to test sent signal and it's providing_args. Signal triggered inside contact_question_create view just after form submission.

My TestCase is something like:

    def test_form_should_post_proper_data_via_signal(self):         form_data = {'name': 'Jan Nowak'}         signals.question_posted.send(sender='test', form_data=form_data)         @receiver(signals.question_posted, sender='test')         def question_posted_listener(sender, form_data):             self.name = form_data['name']         eq_(self.name, 'Jan Nowak') 

Is this the proper way to test this signal? Any better ideas?

Answer 1

Simplest way to do what you asked in 2015:

from unittest.mock import patch  @patch('full.path.to.signals.question_posted.send') def test_question_posted_signal_triggered(self, mock):     form = YourForm()     form.cleaned_data = {'name': 'Jan Nowak'}     form.save()      # Check that your signal was called.     self.assertTrue(mock.called)      # Check that your signal was called only once.     self.assertEqual(mock.call_count, 1)      # Do whatever else, like actually checking if your signal logic did well. 

And with that, you just tested that your signal was properly triggered.

Answer 2

I have an alternative suggestion using the mock library, which is now part of the unittest.mock standard library in Python 3 (if you're using Python 2, you'll have to pip install mock).

try:     from unittest.mock import MagicMock except ImportError:     from mock import MagicMock  def test_form_should_post_proper_data_via_signal(self):     """     Assert signal is sent with proper arguments     """       # Create handler     handler = MagicMock()     signals.question_posted.connect(handler, sender='test')      # Post the form or do what it takes to send the signal     signals.question_posted.send(sender='test', form_data=form_data)      # Assert the signal was called only once with the args     handler.assert_called_once_with(signal=signals.question_posted, form_data=form_data, sender="test") 

The essential part of the suggestion is to mock a receiver, then test whether or not your signal is being sent to that receiver, and called only once. This is great, especially if you have custom signals, or you've written methods that send signals and you want to ensure in your unit tests that they are being sent.