Spring Boot Mockito Support

External

• https://www.baeldung.com/injecting-mocks-in-spring
• https://spring.io/blog/2016/04/15/testing-improvements-in-spring-boot-1-4#mocking-and-spying

Internal

• Spring Boot Testing Concepts
• Mockito

Overview

Spring Boot has built-in Mockito support and no additional dependencies are required in the Gradle build.gradle file to use Mockito mocks. This article describes the minimal amount of steps to inject Mockito mocks in tests, alongside whatever components and real JPA repositories the application uses. Note that a H2-based JPA repository is better than a Mockito mock, because it tests the real persistence logic.

@MockBean

The org.springframework.boot.test.mock.mockito.MockBean annotation injects Mockito mocks built around whatever component is specified in the test. Using @MockBean is the key to easily using mocks from Spring Boot unit tests.

Note that mocks will be automatically reset across tests.

Dependencies

dependencies {
  ...
  testImplementation 'org.springframework.boot:spring-boot-starter-test' // no special Mockito dependency is necessary
}

Testing with @MockBean

Annotate the test with @SpringBootTest. This will automatically allow injections of all real components from the application, including the JPA repositories. This is important, because a H2-based JPA repository is better than a mock.

@SpringBootTest
public class SomeControllerTest {

   //
   // this is the real component to test
   // 
   @Autowired
   private SomeController someController

   //
   // SpringBoot will automatically wrap the component in a Mockito proxy
   // and the mock component will be injected into the tested component
   // 
   @MockBean
   private SomeDependencyComponent someDependencyComponent;

   @Before
   public void configureMocks() {
      //
      // if mock configuration is shared among tests, the configuration can be done in a 
      // @Before method; the mocks will be reset after each test
      //
      when(someDependencyComponent.someMethod()).thenReturn("something");
   }

   @Test
   public void test() {
      //
      // configure the mock in each test, the mocks will be reset after each test
      //
      when(someDependencyComponent.someOtherMethod()).thenReturn("something else");

      //
      // test
      // 
      result = someController.someMethod(...);
      assertEquals(..., result.someStuff());
   }
}