Integration Testing

While unit tests check individual bricks, integration tests check if those bricks fit together to build a wall.

What is an Integration?

An integration is any boundary between two components. This could be:

• Your application and its Database.
• Your frontend and your API.
• Your service and a Third-Party Service (like Stripe or AWS).

The Goal

Integration tests catch bugs that unit tests miss, such as:

• Incorrect database queries.
• Misconfigured API endpoints.
• Incompatible data formats between two services.

Example: Testing a Database Save (Python)

In this example, we aren’t testing the save_user logic itself, but rather that our code can successfully talk to a real (or test) database.

import pytest
from my_app import db, User

def test_db_integration():
    # Arrange: Create a new user
    user = User(username="test_dev", email="test@example.com")
    
    # Act: Save to database
    db.session.add(user)
    db.session.commit()
    
    # Assert: Fetch it back and verify it exists
    retrieved_user = User.query.filter_by(username="test_dev").first()
    assert retrieved_user is not None
    assert retrieved_user.email == "test@example.com"
    
    # Cleanup: Remove the test data
    db.session.delete(retrieved_user)
    db.session.commit()

How it Differs from Unit Testing

Best Practices

1. Use a Test Database: NEVER run integration tests against your production database.
2. Start from a Clean State: Each test should set up its own data and clean up afterward.
3. Test the Happy Path and Errors: Test that the components work together when things go right AND when the database/service is down.

Summary

Integration tests provide higher confidence than unit tests but are harder to maintain. Balance is key.