Testing in Spring Boot

In this article, we will be discussing Testing in Spring Boot. There are so many different testing approaches in Spring Boot used for deploying the application server. Testing in Spring Boot is an important feature of software development which ensures that your application behaves as per the requirement and meets all the testing criteria. Spring Boot provides a robust testing framework that supports Unit Testing, Integration Testing, and End-to-End Testing.

1. Unit Tests:

• The Focus is on testing individual components or units of the code in isolation.
• Use tools like JUnit and Mockito for the writing unit tests.

2. Integration Tests:

• Test the interactions between the multiple components or modules.
• Ensures that different parts of the application work together perfectly.
• Typically involves testing repositories, services, and controllers.

3. End-to-End (E2E) Tests:

• Test the entire application from the end to end simulating real user scenarios.
• Involve testing application's behavior through its external interfaces.
• Use tools like Selenium for the web applications.

Testing Annotations in Spring Boot

@SpringBootTest:

• Indicates that the annotated class is the Spring Boot test.
• The Loads the complete application context.

@SpringBootTest
public class MySpringBootTest {
    // Test methods go here
}

@RunWith(SpringRunner.class):

• The Specifies the class to run the tests.
• The SpringRunner is the alias for SpringJUnit4ClassRunner.

@RunWith(SpringRunner.class)
@SpringBootTest
public class MySpringBootTest {
    // Test methods go here
}

@MockBean:

• The Mocks a Spring Bean for testing purposes.
• Useful for the isolating the unit of the code being tested.

@SpringBootTest
public class MyServiceTest {
    @Autowired
    private MyService myService;
    @MockBean
    private ExternalService externalService;
    // Test methods go here
}

@Test:

• The Denotes a test method.
• Executed when running the test class.

@Test
public void myUnitTest() {
    // Test logic goes here
}

Maven Dependencies for Testing

To get started with the testing in the Spring Boot project you need to include the following dependencies in the your pom.xml file:

<dependencies>
    <!-- Spring Boot Starter Test -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>

JUnit Testing Dependency

The Spring Boot uses JUnit as the default testing framework. The spring-boot-starter-test dependency already includes the JUnit so you don't need to add it explicitly.

<dependency> 
      <groupId>junit</groupId> 
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>test</scope> 
</dependency>

1. @SpringBootTest (Integration Testing)

The @SpringBootTest is a core annotation in Spring Boot for the integration testing. It can be used to the specify the configuration of ApplicationContext for the your tests.

Let's consider a simple controller class:

@RestController
public class MyController {
    @GetMapping("/hello")
    public String hello() {
        return "Hello, World!";
    }
}

Now, let's write a test class:

@RunWith(SpringRunner.class)
@SpringBootTest
public class MyControllerTest {
    @Autowired
    private MockMvc mockMvc;
    @Test
    public void testHelloEndpoint() throws Exception {
        mockMvc.perform(get("/hello"))
                .andExpect(status().isOk())
                .andExpect(content().string("Hello, World!"));
    }
}

Explanation:

• @RunWith(SpringRunner.class):The Specifies the runner that JUnit should use to run the tests. The SpringRunner is the new name for the SpringJUnit4ClassRunner.
• @SpringBootTest: Used to indicate that the annotated class is the Spring Boot test class.

Property File Configuration:

For testing, you might want to have a separate the application-test.properties file. The Spring Boot automatically picks up properties from this file during the tests.

2. @TestConfiguration (Test Configuration)

The @TestConfiguration is used to the specify additional configuration for the tests. It is often used to define @Bean methods for the test-specific beans.

@TestConfiguration
public class TestConfig {
    @Bean
    public MyService myService() {
        return new MyService();
    }
}

3. @MockBean (Mocking)

The @MockBean is used to mock a bean of the specific type, making it convenient to test components that depend on bean.

@RunWith(SpringRunner.class)
@SpringBootTest
public class MyServiceTest {
    @Autowired
    private MyService myService;
    @MockBean
    private ExternalService externalService;
    @Test
    public void testServiceMethod() {
        // Define behavior for the mocked external service
        when(externalService.getData()).thenReturn("Mocked Data");
        // Now test the method from MyService that uses externalService
        String result = myService.processData();
        assertEquals("Processed: Mocked Data", result);
    }
}

4. @WebMvcTest (Unit Testing)

The @WebMvcTest is used for the testing the controllers in the Spring MVC application. It focuses only on MVC components.

@RunWith(SpringRunner.class)
@WebMvcTest(MyController.class)
public class MyControllerWebMvcTest {
    @Autowired
    private MockMvc mockMvc;
    @Test
    public void testHelloEndpoint() throws Exception {
        mockMvc.perform(get("/hello"))
                .andExpect(status().isOk())
                .andExpect(content().string("Hello, World!"));
    }
}

5. @DataJpaTest (Integration Testing)

The @DataJpaTest is used for the testing JPA repositories. It focuses only on the JPA components.

@RunWith(SpringRunner.class)
@DataJpaTest
public class MyRepositoryTest {
    @Autowired
    private MyRepository myRepository;
    @Test
    public void testRepositoryMethod() {
        MyEntity entity = new MyEntity();
        entity.setData("Test Data");
        myRepository.save(entity);
        MyEntity savedEntity = myRepository.findById(entity.getId()).orElse(null);
        assertNotNull(savedEntity);
        assertEquals("Test Data", savedEntity.getData());
    }
}

Additional Annotations

• @AutoConfigureMockMvc: Used with the @SpringBootTest to automatically configure a MockMvc instance.
• @DirtiesContext: Indicates that the ApplicationContext associated with test is dirty and should be closed after the test.
• @Transactional: Used to indicate that a test-managed transaction should be used.

Conclusion

The Spring Boot's testing support combined with the popular testing libraries like JUnit and Mockito enables the developers to create comprehensive test suites for their applications. By using the appropriate testing annotations and strategies you can ensure the reliability and correctness of the your Spring Boot applications.