JUnit 5 + Testcontainers patterns

Choose the smallest scope that covers the AC

AC type	Use
Pure logic (calculator, validator, mapper)	Plain JUnit 5, no Spring
Controller validation, status codes, JSON shape	`@WebMvcTest`
JPA query / mapping	`@DataJpaTest` + Testcontainers (`@ServiceConnection`)
End-to-end through HTTP, with DB / external	`@SpringBootTest(webEnvironment = RANDOM_PORT)` + Testcontainers
Cache, security filter chain, bean wiring	targeted slice (e.g. `@WebMvcTest` + `@Import`)

@SpringBootTest is a last resort. If a slice test can cover it, use the slice.

Every @Test and @ParameterizedTest method MUST carry @DisplayName. No exceptions — write the display name before the test body so articulating it forces clarity about what the test verifies. (Project rule: feedback_displayname_on_every_test.md.)
The full annotation block on every test method is all three lines, in this order: