Difference Between @Mock, @Mockbean and Mockito.Mock()

Difference between @Mock, @MockBean and Mockito.mock()

Plain Mockito library

import org.mockito.Mock;
...
@Mock
MyService myservice;

and

import org.mockito.Mockito;
...
MyService myservice = Mockito.mock(MyService.class);

come from the Mockito library and are functionally equivalent.

They allow to mock a class or an interface and to record and verify behaviors on it.

The way using annotation is shorter, so preferable and often preferred.

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Note that to enable Mockito annotations during test executions, the
MockitoAnnotations.initMocks(this) static method has to be called.

To avoid side effect between tests, it is advised to do it before each test execution :

@Before 
public void initMocks() {
    MockitoAnnotations.initMocks(this);
}

Another way to enable Mockito annotations is annotating the test class with @RunWith by specifying the MockitoJUnitRunner that does this task and also other useful things :

@RunWith(org.mockito.runners.MockitoJUnitRunner.class)
public MyClassTest{...}

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Spring Boot library wrapping Mockito library

This is indeed a Spring Boot class:

import org.springframework.boot.test.mock.mockito.MockBean;
...
@MockBean
MyService myservice;

The class is included in the spring-boot-test library.

It allows to add Mockito mocks in a Spring ApplicationContext.

If a bean, compatible with the declared class exists in the context, it replaces it by the mock.

If it is not the case, it adds the mock in the context as a bean.

Javadoc reference :

Annotation that can be used to add mocks to a Spring
ApplicationContext.

...

If any existing single bean of the same type defined in the context
will be replaced by the mock, if no existing bean is defined a new one
will be added.

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When use classic/plain Mockito and when use @MockBean from Spring Boot ?

Unit tests are designed to test a component in isolation from other components and unit tests have also a requirement : being as fast as possible in terms of execution time as these tests may be executed each day dozen times on the developer machines.

Consequently, here is a simple guideline :

As you write a test that doesn't need any dependencies from the Spring Boot container, the classic/plain Mockito is the way to follow : it is fast and favors the isolation of the tested component.

If your test needs to rely on the Spring Boot container and you want also to add or mock one of the container beans : @MockBean from Spring Boot is the way.

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Typical usage of Spring Boot @MockBean

As we write a test class annotated with @WebMvcTest (web test slice).

The Spring Boot documentation summarizes that very well :

Often @WebMvcTest will be limited to a single controller and used in
combination with @MockBean to provide mock implementations for
required collaborators.

Here is an example :

import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mockito;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.boot.test.mock.mockito.MockBean;
import org.springframework.http.MediaType;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.MockMvc;

import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

@RunWith(SpringRunner.class)
@WebMvcTest(FooController.class)
public class FooControllerTest {

    @Autowired
    private MockMvc mvc;

    @MockBean
    private FooService fooServiceMock;

    @Test
    public void testExample() throws Exception {
         Foo mockedFoo = new Foo("one", "two");

         Mockito.when(fooServiceMock.get(1))
                .thenReturn(mockedFoo);

         mvc.perform(get("foos/1")
            .accept(MediaType.TEXT_PLAIN))
            .andExpect(status().isOk())
            .andExpect(content().string("one two"));
    }

}

When to use and not use @Mock annotation, @MockBean annotation, @InjectMock annotation & @Autowired annotation in a spring webflux reactive project

@Mock

Used to make Mockito create a mock object.

@InjectMock

When you want Mockito to create an instance of an object and use the mocks annotated with @Mock as its dependencies.

@AutoWired

Used when you want to autowire a bean from the spring context, works exactly the same as in normal code but can only be used in tests that actually creates an application context, such as tests annotated with @WebMvcTest or @SpringBootTest.

@MockBean

Can be used to add mock objects to the Spring application context. The mock will replace any existing bean of the same type in the application context. If no bean of the same type is defined, a new one will be added. Often used together with @SpringBootTest

So normally you either:

• Use @Mock and @InjectMocks for running tests without a spring
  context, this is preferred as it's much faster.
• Use @SpringBootTest or @SpringMvcTest to start a spring context together with @MockBean to create mock objects and @Autowired to get an instance of class you want to test, the mockeans will be used for its autowired dependencies. You use this when writing integration tests for code that interact with a database or want to test your REST API.

What is difference here - @Autowired and @MockBean

A @SpringBootTest is a test that actually starts up a Spring container along with the beans of the application.

@Autowired fields in tests behave like they do in normal Spring-Beans; they get injected with the actual beans configured in the application (xml, @Bean in a @Configuration, or @Component/@Service).

@MockBean creates a mock that they behave like normal mocks that you can control with when/then etc and check with verify and suchlike. The thing that is special about them is that they get injected into other beans in the context (for instance when you call Mockito.initAnnotations(this)).

What is difference between @SpyBean and @MockBean in Mockito?

A mock (no matter if we talk about ordinary objects or beans) is simply an "empty shell".

That mock object doesn't have any relation to the underlying production code. It is an object that looks like being an object of class X. But none of the methods or fields that X has do "really" exist on that mocked thing.

Whereas a spy wraps around an existing object of your class under test. Meaning: when you create a spy, you can decide if method calls going to the spy should be "intercepted" (then you are using the spy as if it would be a mock); or be "passed through" to the actual object the spy wraps around.

See here for further reading.

@MockBean and @Autowired of the same service in one test class

The best solution is to change @MockBean to @SpyBean. And in the method you will be able to do like this:

kotlin

    @SpyBean
    lateinit var serviceMock: Service

    @Test
    fun smallTest()
        `when`(serviceMock.doSomething())
            .thenReturn(false)

        // your test logic
    }

What is the difference between mockito-core and mockito-all

mockito-core only contains mockito classes, while mockito-all contain mockito classes as well as some dependencies, one of them being hamcrest.

In fact mockito-all is discontinued according to the mockito website

“mockito-all” distribution has been discontinued in Mockito 2.*.

The two packages were/are equivalent but if you depend on mockito-core you'll need to add a specific dependency on the packages transitively included in mockito-all if you require them in your project.

I've personally experienced some issues when depending on a newer version some hamcrest matchers while at the same time having a dependency on mockito-all.

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