Databases

Testcontainers spins up real databases and services as Docker containers inside your test suite. Tests run against production-grade PostgreSQL, Redis, or Kafka instead of flaky mocks. The testcontainers-python v4.14.2 library works with pytest . It automates the container life cycle. You get isolated, reproducible integration tests that catch bugs unit tests miss.

Below: setup with pytest, testing services beyond databases, performance patterns, and CI/CD configuration.

Why Mocks and In-Memory Databases Are Not Enough

Mocking db.execute() only checks if your code calls the function. It does not check if the SQL is valid. It also misses schema errors and type mismatches. You might have passing tests while your queries fail in production.

Alembic is the standard migration tool for SQLAlchemy projects. You run alembic init, point it at your SQLAlchemy models, and use alembic revision --autogenerate to produce migration scripts. Alembic then applies those scripts in order with alembic upgrade head. You get repeatable, reviewable schema changes that work the same way everywhere your app runs. The latest stable release is Alembic 1.18.4. It supports SQLAlchemy 2.0 (now at 2.0.48) and its modern typed APIs.