Developer Advocates Integration Tests Over Mocks for FastAPI and PostgreSQL

A developer behind CitizenApp, a multi-tenant application with nine AI features in production, has shared a testing approach for FastAPI that prioritizes real database interactions over mocked unit tests. The author argues that mocking databases creates a false sense of security, as transaction isolation issues, cascading deletes, and constraint violations only surface when tests run against an actual PostgreSQL instance. The recommended setup uses pytest fixtures that wrap each test in a database transaction, which is rolled back after completion to keep the test environment clean without dropping tables. A key fixture overrides FastAPI's dependency injection to route test requests through a controlled database session tied to the same connection and transaction. The author acknowledges integration tests are slower than unit tests but contends they are essential for shipping production code with confidence.