Testing Patterns

Write effective, maintainable tests using modern patterns.

Test Structure (AAA Pattern)

def test_user_registration(): # Arrange user_data = {"email": "test@example.com", "password": "secure123"}

# Act
result = register_user(user_data)

# Assert
assert result.success is True
assert result.user.email == "test@example.com"

Mocking External Services

from unittest.mock import Mock, patch

@patch('services.email.send_email') def test_sends_welcome_email(mock_send): mock_send.return_value = True

register_user({"email": "test@example.com"})

mock_send.assert_called_once_with(
    to="test@example.com",
    template="welcome"
)

Fixtures and Factories

import pytest from factories import UserFactory

@pytest.fixture def user(): return UserFactory.create(role="admin")

@pytest.fixture def authenticated_client(user): client = TestClient(app) client.login(user) return client

def test_admin_dashboard(authenticated_client): response = authenticated_client.get("/admin") assert response.status_code == 200

Integration Tests

@pytest.mark.integration def test_full_checkout_flow(db_session, stripe_mock): # Create test data user = create_user() product = create_product(price=100)

# Execute flow
cart = add_to_cart(user, product)
order = checkout(cart, payment_method="card")

# Verify
assert order.status == "completed"
assert stripe_mock.charges.create.called

Test Coverage Goals

• Unit tests: 80%+ coverage

• Integration tests: Critical paths

• E2E tests: Happy paths only