Testing and Production

• Pick the narrowest test that proves the behavior
• spring-boot-starter-test bundles JUnit 5, AssertJ, Mockito, Hamcrest, JSONassert, JsonPath, Spring Test

• Config found by searching upward from the test package for @SpringBootConfiguration
• Keep tests in the same package tree as the main app class

• Which test first? Plain unit test; slice next, full context only if needed
• Default webEnvironment? MOCK, no real server
• Why is the suite slow? Many distinct contexts defeat caching
• Test cannot find config? Move it under the main class's package

• @WebMvcTest(UserController.class) loads only the web layer
• Loaded: controllers, @ControllerAdvice, Filters, Converters, WebMvcConfigurer
• Not loaded: services and repositories
• Supply dependencies with @MockitoBean (Boot 3.4+; @MockBean deprecated before it)
• Missing mock → NoSuchBeanDefinitionException

mockMvc.perform(get("/users/1"))
  .andExpect(status().isOk())
  .andExpect(jsonPath("$.name").value("Ann"));
mockMvc.perform(post("/users")
  .contentType(MediaType.APPLICATION_JSON)
  .content(json));

POST needs contentType, else 415

• Testcontainers runs real Postgres, Kafka, Redis in throwaway Docker containers
• Tests match production; Docker must be running
• Pin image tags, never latest

@SpringBootTest
@Testcontainers
class OrderIT {
  @Container @ServiceConnection
  static PostgreSQLContainer<?> db =
    new PostgreSQLContainer<>("postgres:16");
}

Boot 3.1+: no manual URL

• Add spring-boot-starter-actuator
• Default: only /actuator/health over HTTP
• management.endpoints.web.exposure.include=health,info,metrics,prometheus
• management.server.port keeps probes off the public port

• ./mvnw package or ./gradlew bootJar → executable fat JAR
• Run it: java -jar app.jar
• war only for external servlet containers
• Layered by default (2.4+): dependencies, spring-boot-loader, snapshot-dependencies, application
• Unchanged dependency layers stay cached in Docker

java -Djarmode=tools -jar app.jar extract --layers

splits the JAR into layer folders

• ./mvnw spring-boot:build-image (or bootBuildImage): no Dockerfile needed
• OCI image with JRE, memory calculator, non-root user
• Dockerfile: ENTRYPOINT ["java","-jar","app.jar"]

• 415 = missing contentType
• NoSuchBeanDefinitionException in a slice = missing mock
• Each distinct @MockBean or property set = new cached context