How to use SmartNullPointerException method of org.mockito.exceptions.verification.SmartNullPointerException class

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.

---

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{...}

---

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.

---

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.

---

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"));
    }

}

The following suggestion let's you test abstract classes without creating a "real" subclass - the Mock is the subclass.

use Mockito.mock(My.class, Mockito.CALLS_REAL_METHODS), then mock any abstract methods that are invoked.

Example:

public abstract class My {
  public Result methodUnderTest() { ... }
  protected abstract void methodIDontCareAbout();
}

public class MyTest {
    @Test
    public void shouldFailOnNullIdentifiers() {
        My my = Mockito.mock(My.class, Mockito.CALLS_REAL_METHODS);
        Assert.assertSomething(my.methodUnderTest());
    }
}

Note: The beauty of this solution is that you do not have to implement the abstract methods, as long as they are never invoked.

In my honest opinion, this is neater than using a spy, since a spy requires an instance, which means you have to create an instantiatable subclass of your abstract class.

@InjectMocks is a Mockito mechanism for injecting declared fields in the test class into matching fields in the class under test. It doesn't require the class under test to be a Spring component.

@Autowired is Spring's annotation for autowiring a bean into a production, non-test class.

If you wanted to leverage the @Autowired annotations in the class under test, another approach would be to use springockito which allows you to declare mock beans so that they will be autowired into the class under test the same way that Spring would autowire the bean. But typically that's not necessary.

I changed TestCompile to androidTestCompile and it's worked without problems.

testCompile 'junit:junit:4.12'

to

androidTestCompile 'junit:junit:4.12'

Since you are loading configuration class MyApplication.class datasource bean will be created, Try moving datasource in another bean which is not used in a test, make sure all classes loaded for tests are not dependant on datasource.
Or
In your tests create a config class marked with @TestConfiguration and include it in SpringBootTest(classes=TestConfig.class) mocking data source there like

@Bean
public DataSource dataSource() {
    return Mockito.mock(DataSource.class);
}

But this may fail since method call to this mocked datasouce for connection will return null, In that case, you'll have to create an in-memory datasource and then mock jdbcTemplate and rest of dependencies.

This is typically what a mocking framework can do for you.

With Mockito for instance:

// imports ommited for brevity
@Test
public void callbackIsCalled()
{
    final CallBack callBack = mock(CallBack.class);
    method(callBack);

    verify(callBack, only()).handle(any());
}

Of course, this is an example of verification mode (only()) and value matcher (any()). You can do more...

(other mocking frameworks exist, but I personally find Mockito the easiest to use, in addition to being one of the most powerful)

Update July 29, 2015 by @durron597: This excellent answer was correct in 2013, however it has since been rendered obsolete by an update to Mockito. See this answer.

I use latest JUnit with Mockito core dependency and hamcrest 1.3 in many Maven projects at work. Till now nobody reported any problem with this. So if this works for your tests go with the newest Version for all three. Just ensure to use mockito core instead of all.

So I would recommend to go with option 2 to have all benefits of the newer versions. If you are really in doubt that anything could go wrong use option 4 which is the safest one. But of course you could go with option 2 and when in the near future anything would be wrong you could switch to option 2. Or since then a newer mockito is already out there solving this.

Note from mockito Issue 397: This problem does not appear with mockito-core.

First you need to create a mock m_contractsDao and set it up. Assuming that the class is ContractsDao:

ContractsDao mock_contractsDao = mock(ContractsDao.class);
when(mock_contractsDao.save(any(String.class))).thenReturn("Some result");

Then inject the mock into m_orderSvc and call your method.

m_orderSvc.m_contractsDao = mock_contractsDao;
m_prog = new ProcessOrdersWorker(m_orderSvc, m_opportunitySvc, m_myprojectOrgSvc);
m_prog.work(); 

Finally, verify that the mock was called properly:

verify(mock_contractsDao, times(1)).save("Parameter I'm expecting");

This should work

import static org.mockito.ArgumentMatchers.any;
import static org.mockito.Mockito.verify;

verify(bar).DoStuff(any(Foo[].class));