With 20 integration test classes, each starting its own PostgreSQL container, you pay 20 container starts at 2 seconds each — 40 seconds of pure overhead before a single assertion runs. The singleton pattern starts one container per JVM, shares it across all test classes, and cuts that 40 seconds to 2. This is the most impactful performance optimization for large Testcontainers test suites. What You’ll Learn The singleton pattern using a static initializer block Abstract base class design for sharing containers and @DynamicPropertySource Why you must not combine @Testcontainers/@Container with the singleton pattern Spring TestContext caching — how it works and how to maximize reuse The @ImportTestcontainers approach for Spring Boot 3.