django-tdd

SKILL.md

Django Testing with TDD

Test-driven development for Django applications using pytest, factory_boy, and Django REST Framework.

When to Activate

Writing new Django applications

Implementing Django REST Framework APIs

Testing Django models, views, and serializers

Setting up testing infrastructure for Django projects

TDD Workflow for Django

Red-Green-Refactor Cycle
# Step 1: RED - Write failing test
def test_user_creation():
    user = User.objects.create_user(email='test@example.com', password='testpass123')
    assert user.email == 'test@example.com'
    assert user.check_password('testpass123')
    assert not user.is_staff

# Step 2: GREEN - Make test pass
# Create User model or factory

# Step 3: REFACTOR - Improve while keeping tests green

Setup

pytest Configuration

# pytest.ini
[pytest]
DJANGO_SETTINGS_MODULE = config.settings.test
testpaths = tests
python_files = test_*.py
python_classes = Test*
python_functions = test_*
addopts =
    --reuse-db
    --nomigrations
    --cov=apps
    --cov-report=html
    --cov-report=term-missing
    --strict-markers
markers =
    slow: marks tests as slow
    integration: marks tests as integration tests

Test Settings

# config/settings/test.py
from .base import *

DEBUG = True
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': ':memory:',
    }
}

# Disable migrations for speed
class DisableMigrations:
    def __contains__(self, item):
        return True

    def __getitem__(self, item):
        return None

MIGRATION_MODULES = DisableMigrations()

# Faster password hashing
PASSWORD_HASHERS = [
    'django.contrib.auth.hashers.MD5PasswordHasher',
]

# Email backend
EMAIL_BACKEND = 'django.core.mail.backends.console.EmailBackend'

# Celery always eager
CELERY_TASK_ALWAYS_EAGER = True
CELERY_TASK_EAGER_PROPAGATES = True

conftest.py

# tests/conftest.py
import pytest
from django.utils import timezone
from django.contrib.auth import get_user_model

User = get_user_model()

@pytest.fixture(autouse=True)
def timezone_settings(settings):
    """Ensure consistent timezone."""
    settings.TIME_ZONE = 'UTC'

@pytest.fixture
def user(db):
    """Create a test user."""
    return User.objects.create_user(
        email='test@example.com',
        password='testpass123',
        username='testuser'
    )

@pytest.fixture
def admin_user(db):
    """Create an admin user."""
    return User.objects.create_superuser(
        email='admin@example.com',
        password='adminpass123',
        username='admin'
    )

@pytest.fixture
def authenticated_client(client, user):
    """Return authenticated client."""
    client.force_login(user)
    return client

@pytest.fixture
def api_client():
    """Return DRF API client."""
    from rest_framework.test import APIClient
    return APIClient()

@pytest.fixture
def authenticated_api_client(api_client, user):
    """Return authenticated API client."""
    api_client.force_authenticate(user=user)
    return api_client

Factory Boy

Factory Setup

# tests/factories.py
import factory
from factory import fuzzy
from datetime import datetime, timedelta
from django.contrib.auth import get_user_model
from apps.products.models import Product, Category

User = get_user_model()

class UserFactory(factory.django.DjangoModelFactory):
    """Factory for User model."""

    class Meta:
        model = User

    email = factory.Sequence(lambda n: f"user{n}@example.com")
    username = factory.Sequence(lambda n: f"user{n}")
    password = factory.PostGenerationMethodCall('set_password', 'testpass123')
    first_name = factory.Faker('first_name')
    last_name = factory.Faker('last_name')
    is_active = True

class CategoryFactory(factory.django.DjangoModelFactory):
    """Factory for Category model."""

    class Meta:
        model = Category

    name = factory.Faker('word')
    slug = factory.LazyAttribute(lambda obj: obj.name.lower())
    description = factory.Faker('text')

class ProductFactory(factory.django.DjangoModelFactory):
    """Factory for Product model."""

    class Meta:
        model = Product

    name = factory.Faker('sentence', nb_words=3)
    slug = factory.LazyAttribute(lambda obj: obj.name.lower().replace(' ', '-'))
    description = factory.Faker('text')
    price = fuzzy.FuzzyDecimal(10.00, 1000.00, 2)
    stock = fuzzy.FuzzyInteger(0, 100)
    is_active = True
    category = factory.SubFactory(CategoryFactory)
    created_by = factory.SubFactory(UserFactory)

    @factory.post_generation
    def tags(self, create, extracted, **kwargs):
        """Add tags to product."""
        if not create:
            return
        if extracted:
            for tag in extracted:
                self.tags.add(tag)

Using Factories

# tests/test_models.py
import pytest
from tests.factories import ProductFactory, UserFactory

def test_product_creation():
    """Test product creation using factory."""
    product = ProductFactory(price=100.00, stock=50)
    assert product.price == 100.00
    assert product.stock == 50
    assert product.is_active is True

def test_product_with_tags():
    """Test product with tags."""
    tags = [TagFactory(name='electronics'), TagFactory(name='new')]
    product = ProductFactory(tags=tags)
    assert product.tags.count() == 2

def test_multiple_products():
    """Test creating multiple products."""
    products = ProductFactory.create_batch(10)
    assert len(products) == 10

Model Testing

Model Tests

# tests/test_models.py
import pytest
from django.core.exceptions import ValidationError
from tests.factories import UserFactory, ProductFactory

class TestUserModel:
    """Test User model."""

    def test_create_user(self, db):
        """Test creating a regular user."""
        user = UserFactory(email='test@example.com')
        assert user.email == 'test@example.com'
        assert user.check_password('testpass123')
        assert not user.is_staff
        assert not user.is_superuser

    def test_create_superuser(self, db):
        """Test creating a superuser."""
        user = UserFactory(
            email='admin@example.com',
            is_staff=True,
            is_superuser=True
        )
        assert user.is_staff
        assert user.is_superuser

    def test_user_str(self, db):
        """Test user string representation."""
        user = UserFactory(email='test@example.com')
        assert str(user) == 'test@example.com'

class TestProductModel:
    """Test Product model."""

    def test_product_creation(self, db):
        """Test creating a product."""
        product = ProductFactory()
        assert product.id is not None
        assert product.is_active is True
        assert product.created_at is not None

    def test_product_slug_generation(self, db):
        """Test automatic slug generation."""
        product = ProductFactory(name='Test Product')
        assert product.slug == 'test-product'

    def test_product_price_validation(self, db):
        """Test price cannot be negative."""
        product = ProductFactory(price=-10)
        with pytest.raises(ValidationError):
            product.full_clean()

    def test_product_manager_active(self, db):
        """Test active manager method."""
        ProductFactory.create_batch(5, is_active=True)
        ProductFactory.create_batch(3, is_active=False)

        active_count = Product.objects.active().count()
        assert active_count == 5

    def test_product_stock_management(self, db):
        """Test stock management."""
        product = ProductFactory(stock=10)
        product.reduce_stock(5)
        product.refresh_from_db()
        assert product.stock == 5

        with pytest.raises(ValueError):
            product.reduce_stock(10)  # Not enough stock

View Testing

Django View Testing

# tests/test_views.py
import pytest
from django.urls import reverse
from tests.factories import ProductFactory, UserFactory

class TestProductViews:
    """Test product views."""

    def test_product_list(self, client, db):
        """Test product list view."""
        ProductFactory.create_batch(10)

        response = client.get(reverse('products:list'))

        assert response.status_code == 200
        assert len(response.context['products']) == 10

    def test_product_detail(self, client, db):
        """Test product detail view."""
        product = ProductFactory()

        response = client.get(reverse('products:detail', kwargs={'slug': product.slug}))

        assert response.status_code == 200
        assert response.context['product'] == product

    def test_product_create_requires_login(self, client, db):
        """Test product creation requires authentication."""
        response = client.get(reverse('products:create'))

        assert response.status_code == 302
        assert response.url.startswith('/accounts/login/')

    def test_product_create_authenticated(self, authenticated_client, db):
        """Test product creation as authenticated user."""
        response = authenticated_client.get(reverse('products:create'))

        assert response.status_code == 200

    def test_product_create_post(self, authenticated_client, db, category):
        """Test creating a product via POST."""
        data = {
            'name': 'Test Product',
            'description': 'A test product',
            'price': '99.99',
            'stock': 10,
            'category': category.id,
        }

        response = authenticated_client.post(reverse('products:create'), data)

        assert response.status_code == 302
        assert Product.objects.filter(name='Test Product').exists()

DRF API Testing

Serializer Testing

# tests/test_serializers.py
import pytest
from rest_framework.exceptions import ValidationError
from apps.products.serializers import ProductSerializer
from tests.factories import ProductFactory

class TestProductSerializer:
    """Test ProductSerializer."""

    def test_serialize_product(self, db):
        """Test serializing a product."""
        product = ProductFactory()
        serializer = ProductSerializer(product)

        data = serializer.data

        assert data['id'] == product.id
        assert data['name'] == product.name
        assert data['price'] == str(product.price)

    def test_deserialize_product(self, db):
        """Test deserializing product data."""
        data = {
            'name': 'Test Product',
            'description': 'Test description',
            'price': '99.99',
            'stock': 10,
            'category': 1,
        }

        serializer = ProductSerializer(data=data)

        assert serializer.is_valid()
        product = serializer.save()

        assert product.name == 'Test Product'
        assert float(product.price) == 99.99

    def test_price_validation(self, db):
        """Test price validation."""
        data = {
            'name': 'Test Product',
            'price': '-10.00',
            'stock': 10,
        }

        serializer = ProductSerializer(data=data)

        assert not serializer.is_valid()
        assert 'price' in serializer.errors

    def test_stock_validation(self, db):
        """Test stock cannot be negative."""
        data = {
            'name': 'Test Product',
            'price': '99.99',
            'stock': -5,
        }

        serializer = ProductSerializer(data=data)

        assert not serializer.is_valid()
        assert 'stock' in serializer.errors

API ViewSet Testing

# tests/test_api.py
import pytest
from rest_framework.test import APIClient
from rest_framework import status
from django.urls import reverse
from tests.factories import ProductFactory, UserFactory

class TestProductAPI:
    """Test Product API endpoints."""

    @pytest.fixture
    def api_client(self):
        """Return API client."""
        return APIClient()

    def test_list_products(self, api_client, db):
        """Test listing products."""
        ProductFactory.create_batch(10)

        url = reverse('api:product-list')
        response = api_client.get(url)

        assert response.status_code == status.HTTP_200_OK
        assert response.data['count'] == 10

    def test_retrieve_product(self, api_client, db):
        """Test retrieving a product."""
        product = ProductFactory()

        url = reverse('api:product-detail', kwargs={'pk': product.id})
        response = api_client.get(url)

        assert response.status_code == status.HTTP_200_OK
        assert response.data['id'] == product.id

    def test_create_product_unauthorized(self, api_client, db):
        """Test creating product without authentication."""
        url = reverse('api:product-list')
        data = {'name': 'Test Product', 'price': '99.99'}

        response = api_client.post(url, data)

        assert response.status_code == status.HTTP_401_UNAUTHORIZED

    def test_create_product_authorized(self, authenticated_api_client, db):
        """Test creating product as authenticated user."""
        url = reverse('api:product-list')
        data = {
            'name': 'Test Product',
            'description': 'Test',
            'price': '99.99',
            'stock': 10,
        }

        response = authenticated_api_client.post(url, data)

        assert response.status_code == status.HTTP_201_CREATED
        assert response.data['name'] == 'Test Product'

    def test_update_product(self, authenticated_api_client, db):
        """Test updating a product."""
        product = ProductFactory(created_by=authenticated_api_client.user)

        url = reverse('api:product-detail', kwargs={'pk': product.id})
        data = {'name': 'Updated Product'}

        response = authenticated_api_client.patch(url, data)

        assert response.status_code == status.HTTP_200_OK
        assert response.data['name'] == 'Updated Product'

    def test_delete_product(self, authenticated_api_client, db):
        """Test deleting a product."""
        product = ProductFactory(created_by=authenticated_api_client.user)

        url = reverse('api:product-detail', kwargs={'pk': product.id})
        response = authenticated_api_client.delete(url)

        assert response.status_code == status.HTTP_204_NO_CONTENT

    def test_filter_products_by_price(self, api_client, db):
        """Test filtering products by price."""
        ProductFactory(price=50)
        ProductFactory(price=150)

        url = reverse('api:product-list')
        response = api_client.get(url, {'price_min': 100})

        assert response.status_code == status.HTTP_200_OK
        assert response.data['count'] == 1

    def test_search_products(self, api_client, db):
        """Test searching products."""
        ProductFactory(name='Apple iPhone')
        ProductFactory(name='Samsung Galaxy')

        url = reverse('api:product-list')
        response = api_client.get(url, {'search': 'Apple'})

        assert response.status_code == status.HTTP_200_OK
        assert response.data['count'] == 1

Mocking and Patching

Mocking External Services

# tests/test_views.py
from unittest.mock import patch, Mock
import pytest

class TestPaymentView:
    """Test payment view with mocked payment gateway."""

    @patch('apps.payments.services.stripe')
    def test_successful_payment(self, mock_stripe, client, user, product):
        """Test successful payment with mocked Stripe."""
        # Configure mock
        mock_stripe.Charge.create.return_value = {
            'id': 'ch_123',
            'status': 'succeeded',
            'amount': 9999,
        }

        client.force_login(user)
        response = client.post(reverse('payments:process'), {
            'product_id': product.id,
            'token': 'tok_visa',
        })

        assert response.status_code == 302
        mock_stripe.Charge.create.assert_called_once()

    @patch('apps.payments.services.stripe')
    def test_failed_payment(self, mock_stripe, client, user, product):
        """Test failed payment."""
        mock_stripe.Charge.create.side_effect = Exception('Card declined')

        client.force_login(user)
        response = client.post(reverse('payments:process'), {
            'product_id': product.id,
            'token': 'tok_visa',
        })

        assert response.status_code == 302
        assert 'error' in response.url

Mocking Email Sending

# tests/test_email.py
from django.core import mail
from django.test import override_settings

@override_settings(EMAIL_BACKEND='django.core.mail.backends.locmem.EmailBackend')
def test_order_confirmation_email(db, order):
    """Test order confirmation email."""
    order.send_confirmation_email()

    assert len(mail.outbox) == 1
    assert order.user.email in mail.outbox[0].to
    assert 'Order Confirmation' in mail.outbox[0].subject

Integration Testing

Full Flow Testing

# tests/test_integration.py
import pytest
from django.urls import reverse
from tests.factories import UserFactory, ProductFactory

class TestCheckoutFlow:
    """Test complete checkout flow."""

    def test_guest_to_purchase_flow(self, client, db):
        """Test complete flow from guest to purchase."""
        # Step 1: Register
        response = client.post(reverse('users:register'), {
            'email': 'test@example.com',
            'password': 'testpass123',
            'password_confirm': 'testpass123',
        })
        assert response.status_code == 302

        # Step 2: Login
        response = client.post(reverse('users:login'), {
            'email': 'test@example.com',
            'password': 'testpass123',
        })
        assert response.status_code == 302

        # Step 3: Browse products
        product = ProductFactory(price=100)
        response = client.get(reverse('products:detail', kwargs={'slug': product.slug}))
        assert response.status_code == 200

        # Step 4: Add to cart
        response = client.post(reverse('cart:add'), {
            'product_id': product.id,
            'quantity': 1,
        })
        assert response.status_code == 302

        # Step 5: Checkout
        response = client.get(reverse('checkout:review'))
        assert response.status_code == 200
        assert product.name in response.content.decode()

        # Step 6: Complete purchase
        with patch('apps.checkout.services.process_payment') as mock_payment:
            mock_payment.return_value = True
            response = client.post(reverse('checkout:complete'))

        assert response.status_code == 302
        assert Order.objects.filter(user__email='test@example.com').exists()

Testing Best Practices

DO

Use factories: Instead of manual object creation

One assertion per test: Keep tests focused

Descriptive test names: test_user_cannot_delete_others_post

Test edge cases: Empty inputs, None values, boundary conditions

Mock external services: Don't depend on external APIs

Use fixtures: Eliminate duplication

Test permissions: Ensure authorization works

Keep tests fast: Use --reuse-db and --nomigrations

DON'T

Don't test Django internals: Trust Django to work

Don't test third-party code: Trust libraries to work

Don't ignore failing tests: All tests must pass

Don't make tests dependent: Tests should run in any order

Don't over-mock: Mock only external dependencies

Don't test private methods: Test public interface

Don't use production database: Always use test database

Coverage

Coverage Configuration

# Run tests with coverage
pytest --cov=apps --cov-report=html --cov-report=term-missing

# Generate HTML report
open htmlcov/index.html

Coverage Goals

Component
Target Coverage

Models
90%+

Serializers
85%+

Views
80%+

Services
90%+

Utilities
80%+

Overall
80%+

Quick Reference

Pattern
Usage

@pytest.mark.django_db
Enable database access

client
Django test client

api_client
DRF API client

factory.create_batch(n)
Create multiple objects

patch('module.function')
Mock external dependencies

override_settings
Temporarily change settings

force_authenticate()
Bypass authentication in tests

assertRedirects
Check for redirects

assertTemplateUsed
Verify template usage

mail.outbox
Check sent emails

Remember: Tests are documentation. Good tests explain how your code should work. Keep them simple, readable, and maintainable.