# Testing Patterns

> Unit testing and integration testing best practices

- Skill: `langchain-ai/testing-patterns` (Agent Skill)
- Install (CLI): `npx skillmds@latest add langchain-ai/testing-patterns`
- Raw SKILL.md: https://api.skillmd.com/api/skills/langchain-ai/testing-patterns/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: langchain-ai (https://skillmd.com/u/langchain-ai)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/langchain-ai/testing-patterns

---


# Testing Patterns

Write effective, maintainable tests using modern patterns.

## Test Structure (AAA Pattern)

```python
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

```python
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

```python
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

```python
@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