Test Layer Selection for Spring Applications

Own the decision of which test proves a claim. Layer choice is a cost decision, not a style preference: a fast slice that mocks the query is cheap and worthless, a full context test for a rounding rule is slow and unnecessary.

When to use

• Deciding between a plain unit test, a slice test, a container backed test, and a booted end to end test, or fixing a slice that fails on a missing bean or a missing security configuration.
• Choosing between MockMvc, WebTestClient, TestRestTemplate, and a random port server.
• Managing test data, the @Transactional rollback model, security assertions with spring-security-test, and endpoint contract tests.

When not to use

• Test class structure, naming, parameterization, and tags belong to spring-boot-junit.
• Mock, fake, and spy design belong to spring-boot-mockito.
• Container provisioning, image pinning, and parallelism belong to spring-boot-testcontainers.
• Schema and migration history belong to spring-boot-flyway; pipeline stage gating belongs to spring-boot-ci-cd.

Ownership and sibling boundaries