django-tdd v2.0.0A

Immutable. This exact content never changes and is served at /api/v1/blob/492678843ff4b41e.

---
name: django-tdd
description: Use when testing Django applications with pytest - TDD workflow, pytest-django setup, factory_boy and model-bakery fixtures, DRF API testing, mocking and patching, integration tests, or coverage
metadata:
  author: mte90
  version: 2.0.0
  tags:
    - python
    - django
    - testing
    - pytest
    - tdd
---

# 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

```python
# 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

```ini
# 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

```python
# 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

```python
# 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

```python
# 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

```python
# 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
```

## 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

## 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.

## Testing Pitfalls

### Mocking `connections` imported at module scope

If the code under test does `from django.db import connections` at the top of the file, patch `module_under_test.connections`, not `django.db.connections`. The module bound its own reference at import time and won't see the global patch.

### `patch.object` cannot mock dunders on instances

`patch.object(connections, "__getitem__", ...)` silently fails. Mock at the class level (`patch.object(type(connections), "__getitem__", ...)`) or substitute a wrapper object that defines `__getitem__`.

### Always use timezone-aware datetimes

Naive datetimes trigger `RuntimeWarning` and, when `filterwarnings = ["error"]` is set, fail the suite. Use `django.utils.timezone.now()` or `timezone.make_aware(datetime(...))`.

```python
from django.utils import timezone

# WRONG
started_at = datetime(2025, 1, 1, 12, 0, 0)

# RIGHT
started_at = timezone.now()
started_at = timezone.make_aware(datetime(2025, 1, 1, 12, 0, 0))
```

### `auto_now_add` in tests

A `DateTimeField(auto_now_add=True)` ignores values passed to the constructor. Set the value after `save()`, not before:

```python
invoice = Invoice(customer=c)
invoice.save()
invoice.issued_at = some_time
invoice.save()
```

## Deep Dives

Load these reference files for detailed coverage of specific testing areas:

- **Model & View Testing** — `references/model-view-testing.md` — Model tests, view tests, authentication checks
- **DRF API Testing** — `references/drf-api-testing.md` — Serializer tests, ViewSet tests, API endpoints
- **Mocking & Integration** — `references/mocking-integration.md` — External service mocking, email testing, full flow tests
- **Ecosystem & Coverage** — `references/ecosystem-coverage.md` — model-bakery, django-test-migrations, django-test-plus, coverage goals