Unit-testing for mails


This package provides a solid and proven way of unit-testing your emails. If you want to build your emails in a robust way in the first place, read up how in the section “Mailing”.

Side note: This part was also published as a blog article at Medium.

At first, initialise the class in your testing class. Because the class itself behaves more or less like a singleton you can do this in the setupTestData(). It will be executed only once per test class and — compared to setUp() — not for every test.

from ai_django_core.mail.services.tests import EmailTestService
from django.test import TestCase

class MyTestClass(TestCase):

    def setUpTestData(cls):
        cls.email_test_service = EmailTestService()

Now you can use the service in all of your tests. If you know that you want to test emails in several classes, it makes sense to create a base test class which the other classes inherit from.

Querying for emails

To provide a djangoesque look-and-feel, our test service can query the mail outbox for certain criteria.

The easiest thing to do is get all emails:

list_of_emails = self.email_test_service.all()

Maybe you want a specific one? You can filter for a given subject by using a string or a regular expression. Additionally, you can filter for a recipient, the to, cc and bcc attributes:

import re

# Get all mails with given subject
my_email = self.email_test_service.filter(subject='Nigerian prince')

# Get all mails with given subject using a regular expression
my_email = self.email_test_service.filter(subject=re.compile('Ni(.*) prince'))

# Get all mails with given to-recipient
my_email = self.email_test_service.filter(to='foo@bar.com')

Of course, you can connect filters as well:

my_email = self.email_test_service.filter(
    subject='Nigerian prince',

Once you have a queryset of emails — meaning the result of one of the queries above — you can work with it.

You can count the results, especially good for assertions:

# Count the number of results
quantity = self.email_test_service.all().count()

Do you need the first or last element in the list?

# Get first item in list
first_mail = self.email_test_service.filter(subject='Nigerian prince').first()

# Get last item in list
last_mail = self.email_test_service.filter(subject='Nigerian prince').last()

It is very common that you expect one specific email, and you want to know if your mail queryset contains exactly this element. So there is a helper function for this, too:

# Returns `True` if the queryset contains exactly one item
self.email_test_service.filter(subject='Nigerian prince').one()

If you want to access a specific index, you can access it like a queryset:

# Fetch the second email
self.email_test_service.filter(subject='Nigerian prince')[1]

# Fetch the next-to-last email
self.email_test_service.filter(subject='Nigerian prince')[-2]

Assertion helpers

Usually, there are only a couple of ways you can blackbox-test emails. You want to ensure the subject, recipient or content functions the way you expect it to be.

That’s why the class provides some shortcuts which wrap the assertion.

  1. You want to check for exactly one result?

  1. Do you want to check the quantity of found emails?

expected_number_of_emails = 1
  1. Do you want to check the subject?

self.email_test_service.filter(to='foo@bar.com')[0].assert_subject('Reset password')

Finally, we have a look at the content of the email. As you probably know, an email object consists of two parts. A plain-text and an HTML part. To avoid checking two times, the wrapper assert_body_contains() checks in both parts and fails if the given string is missing in one of them.

  1. You want to check if a certain string is included in the body?

  1. Sometimes you want to check if something is NOT part of the body…


To make your life a little easier and happier, each of these methods takes an optional parameter msg which is passed to the assertion and will be shown if it goes sideways. Here is an example:

self.email_test_service.filter(to='foo@bar.com')[0].assert_body_contains('inheritance', msg='Missing words!')



This test case mixin helps out when unit-testing a view. It provides methods for the three main ways to request a view: get, post and delete. Authentication and the creation of the request is handled internally.

class MyViewTestCase(ClassBasedViewTestMixin, TestCase):
    view_class = views.MyView

    def test_get_call_authenticated(self):
        response = self.get(user=self.user, url_params={'pk': 17})
        self.assertEqual(response.status_code, 200)

    def test_get_call_not_authenticated(self):
        response = self.get(user=None, url_params={'pk': 17})
        self.assertEqual(response.status_code, 403)

    def test_post_call(self):
        response = self.post(user=self.user, data={'foo': 'bar'}, url_params={'pk': 17})
        self.assertEqual(response.status_code, 200)

    def test_delete_call(self):
        response = self.delete(user=self.user, url_params={'pk': 17})
        self.assertEqual(response.status_code, 202)


In many cases you will find yourself in the position that you need a request in your unittests. A wise programmer will of course try to avoid looping the request object through all services - but from time to time you just end up with a well written method which takes the request as a parameter.

For these cases the toolbox provides a handy mixin, from which you can easily derive your test class. Then you will be able to use a method called get_request(user=None). If you specify a user, he/she will be the request user. In most cases you won’t need to set an explicit url, so / will be taken as a default. If you do need it, just pass set the url parameter.

from django.test import TestCase
from ai_django_core.tests.mixins import RequestProviderMixin

class MyAwesomeTest(RequestProviderMixin, TestCase):

    def test_something_with_a_request_without_a_user(self):
        request = self.get_request(None)

    def test_something_with_a_request_having_a_user(self):
        request = self.get_request(user=my_user)

    def test_something_with_a_request_with_set_url(self):
        request = self.get_request(url='/path/to/something')


Please refer to the view layer section to get details about how to use this view test mixin.


If you’re working with Django views, you might want to use (and therefore test) the Django messaging framework. To make this as easy as possible, just inherit your view test class from the DjangoMessagingFrameworkTestMixin.

You can either check for a full message or just for a partial one.

from django.test import TestCase
from ai_django_core.tests.mixins import DjangoMessagingFrameworkTestMixin

class MyViewTest(DjangoMessagingFrameworkTestMixin, TestCase):

    def test_my_message_full_case(self):
        # The view creates a message: "It's sunny on Sundays."
        view = function_to_instantiate_your_view()
            view.request, "It's sunny on Sundays.")

    def test_my_message_partial_case(self):
        # The view creates a message: "I have added *n* new records" with "n" being a variable
        view = function_to_instantiate_your_view()
            view.request, 'I have added')

Test structure validator


When working in a Django project, it can happen very easily that you create unit-tests in a way that they won’t be auto-discovered. The mean thing about this is that you can still run those tests - so it’s hard to find those issues.

The most common mistakes are forgetting the __init__.py in the directory or not prefixing your python files with test_. To tackle this problem, we created a handy management command you can run manually or integrate in your CI pipeline.

python manage.py validate_test_structure


You can define all of those settings variables in your main Django settings file.








Filenames which will be ignored, will always ignore __init__




Root path to your application (BASE_DIR in a vanilla Django setup)




Directory where all your Django apps live in, can be set to “”.




List of all your Django apps you want to validate




Directories which will be ignored, will always ignore __pycache__