Spring Study Guide – Testing

Do you use Spring in a unit test?

You don’t necessarily need spring for unit tests.

public class SidecarApiNotificationApplicationTests {
        UserService userService;

        public void testLoadAllUsers() {

          List<User> users = userService.getAllUsers();


What type of tests typically use Spring?

  • Spring provides mock objects and testing support classes for Unit Testing.
    • Tests one unit of functionality
    • Keeps dependencies minimal
    • Isolate from the environment (including Spring)
  • Spring provides first-class support for integration testing.
    • Tests the interaction of multiple units working together
    • Integrates infrastructure like database

How can you create a shared application context in a JUnit integration test?

Spring’s integration testing support has the following primary goals:

  • To manage Spring IoC container caching between tests. By default, once loaded, the configured ApplicationContext is reused for each test.
  • To provide Dependency Injection of test fixture instances.
  • To provide transaction management appropriate to integration testing.
  • To supply Spring-specific base classes that assist developers in writing integration tests.

To access the Context with the TestContext Framework in JUnit, two options to access the managed application context.

1. The first option is by implementing the ApplicationContextAware interface or using @Autowired on a field of the ApplicationContext type. You can specify this in the @RunWith annotation at the class level.

 @ContextConfiguration(classes = BankConfiguration.class) 
 public class AccountServiceJUnit4ContextTests implements ApplicationContextAware { }
  • The SpringRunner class, which is an alias for SpringJUnit4ClassRunner, is a custom JUnit runner helping to load the Spring ApplicationContext by using @ContextConfiguration(classes=AppConfig.class). In JUnit, you can simply run your test with the test runner SpringRunner to have a test context manager integrated.
  • By default, the application context will be cached and reused for each test method, but if you want it to be reloaded after a particular test method, you can annotate the test method with the @DirtiesContext annotation so that the application context will be reloaded for the next test method.
  • Inject Test Fixtures with the TestContext Framework in JUnit. In JUnit, you can specify SpringRunner as your test runner without extending a support class.
  @ContextConfiguration(classes = BankConfiguration.class) 
  public class AccountServiceJUnit4ContextTests { }

2. The second option to access the managed application context is by extending the TestContext support class specific to JUnit: AbstractJUnit4SpringContextTests.

Note that if you extend this support class, you don’t need to specify SpringRunner in the @RunWith annotation because this annotation is inherited from the parent.

@ContextConfiguration(classes = BankConfiguration.class) 
 public class AccountServiceJUnit4ContextTests extends AbstractJUnit4SpringContextTests { }

When and where do you use @Transactional in testing?

  1. At method level: the annotated test method(s) will run, each in its own transaction. By default, automatically rolled back after completion of the test.You can alter this behavior by disabling the defaultRollback attribute of @TransactionConfiguration.
  2. At class level: each test method within that class hierarchy runs within a transaction.You can override this class-level rollback behavior at the method level with the @Rollback annotation, which requires a Boolean value, @Rollback(false), This is equivalent to another annotation introduced in Spring @Commit.

How are mock frameworks such as Mockito or EasyMock used?

Mockito lets you write tests by mocking the external dependencies with the desired behavior. Mock objects have the advantage over stubs in that they are created dynamically and only for the specific scenario tested.

Steps of using Mockito:

  1. Declare and create the mock
  2. Inject the mock
  3. Define the behavior of the mock
  4. Test
  5. Validate the execution
public class SimpleReviewServiceTest { 

  private ReviewRepo reviewMockRepo = mock(ReviewRepo.class); // (1)
  private SimpleReviewService simpleReviewService;
  public void setUp(){
    simpleReviewService = new SimpleReviewService();
    simpleReviewService.setRepo(reviewMockRepo); //(2)
  public void findByUserPositive() {
    User user = new User();
    Set<Review> reviewSet = new HashSet<>();
    when(reviewMockRepo.findAllForUser(user)).thenReturn(reviewSet);// (3)
    Set<Review> result = simpleReviewService.findAllByUser(user); // (4)
    assertEquals(result.size(), 1); //(5)

Mockito with Annotations

  • @Mock : Creates mock instance of the field it annotates
  • @InjectMocks has a behavior similar to the Spring IoC, because its role is to instantiate testing object instances and to try to inject fields annotated with @Mock or @Spy into private fields of the testing object.
  • Use Mockito
    • Either: @RunWith(MockitoJUnitRunner.class) to initialize the mock objects.
    • OR: MockitoAnnotations.initMocks(this) in the JUnit @Before method.
public class MockPetServiceTest {

  SimplePetService simplePetService;
  PetRepo petRepo;
  public void initMocks() { 
  @Test p
  ublic void findByOwnerPositive() { 
    Set<Pet> sample = new HashSet<>(); 
    sample.add(new Pet()); 
    Set<Pet> result = simplePetService.findAllByOwner(owner); 
    assertEquals(result.size(), 1); }

Mockito in Spring Boot


  • It is a Spring Boot annotation,
  • used to define a new Mockito mock bean or replace a Spring bean with a mock bean and inject that into their dependent beans.
  • The annotation can be used directly on test classes, on fields within your test, or on @Configuration classes and fields.
  • When used on a field, the instance of the created mock is also injected
  • Mock beans will be automatically reset after each test method.
  • If your test uses one of Spring Boot’s test annotations (such as @SpringBootTest), this feature is automatically enabled.

How is @ContextConfiguration used?

In spring-test library, @ContextConfiguration is a class-level annotation, that defines the location configuration file, which will be loaded for building up the application context for integration tests.

if @ContextConfiguration is used without any attributes defined, the default behavior of spring is to search for a file named {testClassName}-context.xml in the same location as the test class and load bean definitions from there if found.

@ContextConfiguration(classes={KindergartenConfig.class, HighschoolConfig.class}) @ActiveProfiles("kindergarten") 
public class ProfilesJavaConfigTest {

  FoodProviderService foodProviderService;

Spring Boot provides a @SpringBootTest annotation, which can be used as an alternative to the standard spring-test @ContextConfiguration annotation when you need Spring Boot features. The annotation works by creating the ApplicationContext used in your tests through SpringApplication.

@SpringBootTest(properties = "spring.main.web-application-type=reactive") 
public class MyWebFluxTests { }

How does Spring Boot simplify writing tests?

spring-boot-starter-test pulls in the following all within test scope:

  • JUnit: De-facto standard for testing Java apps
  • JSON Path: XPath for JSON
  • AssertJ: Fluent assertion library
  • Mockito: Java mocking library
  • Hamcrest: Library of matcher objects
  • JSONassert: Assertion library for JSON
  • Spring Test and Spring Boot Test: Test libraries provided by the Spring Framework and Spring Boot.

What does @SpringBootTest do? How does it interact with @SpringBootApplication and @SpringBootConfiguration?

Spring Boot features like loading external properties and logging, are available only if you create ApplicationContext using the SpringApplication class, which you’ll typically use in your entry point class. These additional Spring Boot features won’t be available if you use @ContextConfiguration.

@SpringBootTest uses SpringApplication behind the scenes to load ApplicationContext so that all the Spring Boot features will be available.

  1. If no ContextLoader is specified with @ContextConfiguration, it uses org. springframework.boot.test.context.SpringBootContextLoader by default.
  2. Automated search for a Spring Boot configuration when nested @Configuration classes are used.
  3. Loading environment-specific properties via the properties attribute.
  4. Registering a org.springframework.boot.test.web.client.TestRestTemplate bean for use in web tests that use a fully running container.
  webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT, 
  properties = {"app.port=9090"}) 
public class CtxControllerTest { }
How to define a testing class in Spring?

In order to define a test class for running in a Spring context, the following have to be done:

  1. annotate the test class with @RunWith(SpringJUnit4ClassRunner.class)
  2. annotate the class with @ContextConfiguration in order to tell the runner class where the bean definitions come from
  3. use @Autowired to inject beans to be tested.

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