What is Spring Boot testing strategies?

Spring Boot testing pyramid: 1. Unit tests (no Spring context): test individual classes in isolation using Mockito. No Spring overhead: @ExtendWith(MockitoExtension.class) class UserServiceTest { @Mock UserRepository userRepository; @InjectMocks UserService userService; @Test void shouldCreateUser() { when(userRepository.save(any())).thenReturn(new User("Alice", "alice@example.com")); User result = userService.create("Alice", "alice@example.com"); assertThat(result.getName()).isEqualTo("Alice"); verify(userRepository).save(argThat(u -> u.getEmail().equals("alice@example.com"))); } }. 2. Slice tests (partial Spring context): @WebMvcTest (controller + MockMvc), @DataJpaTest (JPA layer only, H2), @DataMongoTest, @JsonTest (Jackson serialization only). Much faster than full context. 3. Integration tests (full context): @SpringBootTest loads everything. Use Testcontainers for real databases: @SpringBootTest @Testcontainers class OrderIntegrationTest { @Container static PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:15"); @DynamicPropertySource static void registerProperties(DynamicPropertyRegistry registry) { registry.add("spring.datasource.url", postgres::getJdbcUrl); } @Test void shouldCreateOrder() { ... } }. 4. MockMvc for controller tests: mockMvc.perform(post("/api/users").contentType(MediaType.APPLICATION_JSON).content(objectMapper.writeValueAsString(request))).andExpect(status().isCreated()).andExpect(jsonPath("$.email").value("alice@example.com"));. Best practices: test behavior not implementation; prefer @DataJpaTest over mocking repository; use @MockBean sparingly; test error scenarios and edge cases.