Testcontainers spins up real Docker containers for your tests — a real PostgreSQL database, a real Redis, a real Kafka broker. No more mocking JDBC connections or in-memory H2 databases that behave differently from production. Spring Boot 3.1 added @ServiceConnection, which removes the boilerplate of configuring connection URLs manually. This guide covers the right patterns for fast, reliable integration tests with Testcontainers. Why Testcontainers Over H2 Teams use H2 in-memory databases for testing because it’s fast.

The CI pipeline from Article 19 validates migrations against a MySQL service container. But that’s not the same as testing that your application code works correctly after the migration runs. This article covers how to structure Spring Boot tests that validate both the migration and the application behaviour — and makes the case for replacing H2 with Testcontainers as your primary testing database. Three Testing Strategies Strategy Database Speed Fidelity Use For H2 in-memory H2 (in-memory) Fastest Low — MySQL-specific SQL fails Unit tests that mock repositories H2 with MySQL mode H2 (MySQL compat) Fast Medium — most SQL works, some quirks Basic integration tests on simple schemas Testcontainers Real MySQL 8.