Przemek Lewandowski

@haxoza

The Ultimate

(Django)

Testing

About me

Overview

• Unit Testing
• Good practices
• Mocking
• Django Test Cases
• Data Factories
• Django Views Unit Testing
• Integration Testing

Why Unit Testing?

• Finds issues early
• Isolation
• Fast in execution
• Red / Green Refactor
• Architecture
• Live documentation

Why Unit Testing?

Python is dynamically typed language

so

let's execute the code before running on production

Why Unit Testing?

We are programmers

so

let's automate

Common structures

• Tests
• Test Cases
• Suites
• xUnit family

Is your unit testing real unit testing?

Read more here:

http://martinfowler.com/bliki/UnitTest.html

Good practices

Technical perfection

Meaningful names

Read more here:

http://stackoverflow.com/questions/96297/what-are-some-popular-naming-conventions-for-unit-tests

Test Cases names

[name of unit being tested]Tests

    class LoginViewTests(unittest.TestCase):
        pass

Test names

test_[feature being tested]_[expected behaviour]

    def test_post_should_login_user(self):
        pass

Test body structure

Given When Then

• Given: state of the world before the test
• When: behaviour that you're specifying
• Then: changes expected due to the specified behaviour

Read more here:

http://martinfowler.com/bliki/GivenWhenThen.html

Given When Then

    def test_post_should_set_new_username(self):
        # Given

        # When

        # Then

Given When Then

    def test_post_should_set_new_username(self):
        user = create_user()
        data = {
            'new_username': 'ringo',
            'current_password': 'secret',
        }
        request = self.factory.post(user=user, data=data)

        response = self.view(request)

        self.assert_status_equal(response, status.HTTP_200_OK)
        user = utils.refresh(user)
        self.assertEqual(data['new_username'], user.username)

Other good practices

• Short tests (LOC)
• Clean code obliges
• Don't overuse setup method
• Don't hit external services

Dependency injection

Mocking to the rescue

    @mock.patch('stripe.Charge.create')
    def test_post_should_return_error(self, stripe_create_mock):
        stripe_create_mock.side_effect = stripe.StripeError()
        lead_offer = factories.LeadOfferFactory()
        request = self.factory.post(data={'token': 'wrong-token'})

        response = self.view(request, slug=lead_offer.slug)

        self.assert_status_equal(response, status.HTTP_400_BAD_REQUEST)
        self.assert_emails_in_mailbox(0)

unittest.mock in Python 3

Testing in Django

Testing in Django

• Models
• Forms
• Views
• ...

Models testing

• Isolation from views
• State should represent business logic
• Sometimes don't need to hit database

Models instantiation

Models instantiation

• Model Managers
• Factories (Factory Boy)
• Fake data (Faker)

Factory Boy

class UserFactory(factory.DjangoModelFactory):
    FACTORY_FOR = auth.get_user_model()

    email = factory.Sequence(lambda n: 'user-{0}@example.com'.format(n))
    password = 'pass'

    @classmethod
    def _prepare(cls, create, **kwargs):
        password = kwargs.pop('password', None)
        user = super(UserFactory, cls)._prepare(create, **kwargs)
        if password:
            user.raw_password = password
            user.set_password(password)
            if create:
                user.save()
        return user

Factory Boy

    # Don't hit database
    user = UserFactory.build()

    # Hit database
    user = UserFactory.create()

Django specific
Test Cases

django.tests.TestCase

• Rolls back the transaction at the end of the test
• Additional assertions
• Creates instance of django.tests.Client
• The ability to run tests with modified settings
• setUpTestData since Django 1.8

django.tests.testcases

Views testing

Views testing

• django.tests.TestCase

• django.tests.Client

• django.tests.RequestFactory

django.tests.Client

• Runs as fake browser
• Integrated with django.contrib.auth
• Invokes all Django layers
• Mainly for integration testing

Django Middlewares

django.tests.RequestFactory

• Calling the view manually
• Middlewares are skipped
• Hope for real view unit tests 
• Not so easy in use

Common issues 

• Integration vs. unit tests
• All application layers
• Strongly coupled components
• Execution time of middlewares
• Mocking Django backends

Djet

to the rescue

Django Extended Tests

https://github.com/sunscrapers/djet

Star please!

Djet Features

• Easy views unit testing
• Supports function- and class-based views
• Runs only explicite passed middlewares

Djet in action

class YourViewTest(assertions.StatusCodeAssertionsMixin,
                   assertions.MessagesAssertionsMixin,
                   testcases.ViewTestCase):
    view_class = YourView
    view_kwargs = {'some_kwarg': 'value'}
    middleware_classes = [
        SessionMiddleware,
        (MessageMiddleware, testcases.MiddlewareType.PROCESS_REQUEST),
    ]

    def test_post_should_redirect_and_add_message_when_next_parameter(self):
        user = UserFactory()
        request = self.factory.post(data={'next': '/'}, user=user)

        response = self.view(request)

        self.assert_redirect(response, '/')
        self.assert_message_exists(request, messages.SUCCESS, 'Success!')

Other features

• Easier operations on files (in memory)
• Adds extra assertions
• Supports django.contrib.auth
• Supports Django Rest Framework

Djet combo

class TestModel(models.Model):
    field = models.CharField(max_length=100)
    file = models.FileField(upload_to='files')

class CreateAPIView(generics.CreateAPIView):
    model = models.TestModel

class CreateAPIViewTest(assertions.StatusCodeAssertionsMixin,
                        files.InMemoryStorageMixin,
                        restframework.APIViewTestCase):
    view_class = CreateAPIView

    def test_post_should_create_model(self):
        data = {
            'field': 'test value',
            'file': files.create_inmemory_file('test.txt', content=b'Hello multipart!'),
        }
        request = self.factory.post(data=data, format='multipart')

        response = self.view(request)

        self.assert_status_equal(response, status.HTTP_201_CREATED)

Why to use Djet?

• Compact view tests
• Faster execution
• Fixed default FileStorage

Faster execution

Integration testing

Mocking everything out?

    DATABASES = {
        'default': {
            'ENGINE': 'django.db.backends.sqlite3',
        }
    }

    CACHES = {
        'default': {
            'BACKEND': 'django.core.cache.backends.dummy.DummyCache',
        }
    }

Use real dependencies

Continuous Integration

with real database