spring-boot-testing

Use @WebMvcTest for controller and HTTP semantics, @DataJpaTest for repository queries and JPA mappings, and @SpringBootTest only for full integration flows. The rule is to pick the narrowest slice that still gives confidence, keeping the suite fast.

Annotate the test with @DataJpaTest, @Testcontainers, and @AutoConfigureTestDatabase(replace = NONE), then declare a static PostgreSQLContainer with @Container and @ServiceConnection. Use TestEntityManager to persist and flush test data before asserting query results.

In Spring Boot 3.3 use classic MockMvc with perform() and andExpect(), since MockMvcTester requires Spring Boot 3.4 or later. The same applies to @MockBean versus @MockitoBean, which only exists from 3.4 onward.

Yes, @DataJpaTest uses an embedded H2 database by default, which can miss database-specific behavior. Replacing it with a Testcontainers PostgreSQL instance gives parity with production and supports features like JSONB columns.

Slowness usually comes from loading many distinct application contexts. Group tests by identical configuration, minimize @TestPropertySource variations, avoid @DirtiesContext, and prefer narrow slices so the Spring context cache is reused.

Use Instancio when entities or DTOs have three or more properties, to avoid repetitive builder or setter calls. Set only the fields relevant to the test and let Instancio fill the rest with valid random data.