Tutorial Series Part 5: Testing and Deploying the Application

Date: February 18, 2025

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Testing and deployment are the final critical steps to ensure your Spring Boot application is reliable, maintainable, and production-ready. In this tutorial, we’ll cover:

• Writing unit and integration tests with JUnit 5 and Mockito
• Testing Spring MVC controllers and service layers
• Using Spring Boot Test utilities for application context and slices
• Best practices for automated testing
• Preparing your app for deployment
• Packaging as a Docker container
• Basic deployment strategies

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1. Writing Unit Tests with JUnit 5 and Mockito

Unit tests validate small, isolated components like services or utilities.

Example: Testing a UserService

@ExtendWith(MockitoExtension.class)
public class UserServiceTest {

    @Mock
    private UserRepository userRepository;

    @InjectMocks
    private UserService userService;

    @Test
    void whenFindUserById_thenReturnUser() {
        User user = new User(1L, "test@example.com", "Test User");
        Mockito.when(userRepository.findById(1L)).thenReturn(Optional.of(user));

        User found = userService.findById(1L);

        assertNotNull(found);
        assertEquals("test@example.com", found.getEmail());
    }
}

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2. Integration Testing Controllers

Integration tests load the Spring context and test controllers, repositories, and services working together.

Example: Testing UserController with MockMvc

@SpringBootTest
@AutoConfigureMockMvc
public class UserControllerIntegrationTest {

    @Autowired
    private MockMvc mockMvc;

    @Test
    void whenGetUser_thenReturnsJson() throws Exception {
        mockMvc.perform(get("/api/users/1")
                .accept(MediaType.APPLICATION_JSON))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.email").value("test@example.com"));
    }
}

Use @MockBean to mock dependencies if needed.

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3. Using @SpringBootTest and @WebMvcTest

• @SpringBootTest: loads full application context, good for end-to-end tests
• @WebMvcTest: loads only web layer, good for testing controllers in isolation

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4. Best Practices for Testing

• Write tests alongside development
• Use assertions liberally to check behavior
• Mock external dependencies (DB, external APIs)
• Automate tests in CI/CD pipeline (GitHub Actions, Azure Pipelines)
• Keep tests fast and independent

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5. Packaging the Application for Deployment

Spring Boot apps are packaged as fat JARs:

./mvnw clean package

This generates an executable JAR (e.g., demoapp-0.0.1-SNAPSHOT.jar).

Run it with:

java -jar demoapp-0.0.1-SNAPSHOT.jar

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6. Containerizing with Docker

Create a simple Dockerfile:

FROM eclipse-temurin:17-jre-alpine
ARG JAR_FILE=target/demoapp-0.0.1-SNAPSHOT.jar
COPY ${JAR_FILE} app.jar
ENTRYPOINT ["java", "-jar", "/app.jar"]

Build and run your container:

docker build -t demoapp .
docker run -p 8080:8080 demoapp

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7. Deployment Options

• Deploy to cloud providers like AWS Elastic Beanstalk, Azure App Service, Google Cloud Run
• Use container orchestration with Kubernetes for scalable deployments
• Automate deployments with CI/CD pipelines

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Summary

• Developed unit and integration tests with JUnit 5, Mockito, and Spring Boot Test
• Explored packaging and running Spring Boot applications
• Created Docker containers for easy deployment
• Highlighted modern deployment strategies

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Congratulations!

You’ve built, secured, tested, and deployed a full-featured Spring Boot 3 app using modern Java 17 features. Stay tuned for more advanced topics and deep dives!