How to use should_return_empty_iterable method of org.mockito.internal.stubbing.defaultanswers.ReturnsMocksTest class

Why do you need spring to do unit testing? You can only use Mockito to do so without the need to start spring context. This is explained and discussed in details here: https://reflectoring.io/unit-testing-spring-boot/

It's also very confusing for me when it comes to using @MockBean! Is that considered a unit or an integration test? In my opinion, even we're using a mocked bean, but we're still running within spring context and for me this is an integration test (as a unit test doesn't need any spring context to run within). Same site that Brandon mentioned considers @MockBean an integration test https://www.baeldung.com/java-spring-mockito-mock-mockbean.

Image from above site

From Brandon response: "Integration tests should not contain any mocking and both types of testing should be run separately."

What if you want to test an api starting from the controller all the way to DB, but you want to exclude other systems (like kafka or external Microservices)? How would you achieve this? You definitely need @MockBean. This is an integration test even it has mocked beans.

In summary (based on my experience and after searching and reading a lot of contradicting info for days). Here is my opinion:

• I would say, stay away from using spring for unit testing as much as possible and just use Mockito or another framework that doesn’t need spring context. For example, when writing a test for a service class to test some calculation logic, we don’t need spring context and this is a PURE unit test.
• We still can write PURE unit tests for controller classes. We can do that by calling the methods in the controller, then assert that these methods did what is expected (e.g. calling the right underlying methods with correct parameters ..etc). Basically the same way when writing a unit test for a service class. (Maybe these aren’t needed if it’s already gonna be covered in the following types of tests?)
• We still can write pure unit tests for apis without any spring context. This described here. I tried and it worked for me. I'll paste the code at the end of the post.
• When running a test in spring context, this is considered an integration test even if you're using @MockBean. An example of this: if we want to test an api starting from the controller all the way to the DB, but we want to exclude other systems (like kafka, email, or other external Microservices). How would we achieve this? We definitely need @MockBean. This is an integration test even though it uses some mocked beans.

• I think the most confusing part is when testing the api layer only using spring as UserControllerTest in the question does (I mean by that calling the api and making sure it returns the right status code and response format). Is that considered a unit test or an integration test? It is not a unit as unit tests don’t need spring context to run within. It is actually something in between unit and integration tests. This source explains this concept very well https://blog.marcnuri.com/mockmvc-spring-mvc-framework/ (more specifically MockMvc standalone setup) So I think, it goes back then to the team where to place these tests (in the unit test folder, in the integration test folder, in a separate folder?) Also a good naming convention is needed to be used to avoid any confusion with pure unit tests or pure integration tests for the same class. From what I saw, most teams consider those unit tests, but I am not sure if that is the best practice!

  //unit test to call an api using MockMvc and mockito only
  @RunWith(MockitoJUnitRunner.class)
  public class UserControllerTest {
  
  private MockMvc mockMvc;
  @Mock
  UserService userService;
  @InjectMocks
  UserController controllerUnderTest;
  
  @Before
  public void setup() {
      MockitoAnnotations.initMocks(this);
      mockMvc = MockMvcBuilders.standaloneSetup(controllerUnderTest).build();
  }
  
  @Test
  public void testGetUser() throws Exception {
  
      //given:
      when(userService.getUser(.......)).thenReturn(....);
  
      //when:
      String url = "http://localhost:8081/api/ ....your url";
  
      //then:
      this.mockMvc.perform(get(url)).andDo(print()).andExpect(status().isOk());
  }
  

  }

Hope that helps and please let me know if there is any better opinion because I struggled a lot with that :)

You can do that:

doThrow(...).doNothing().when(mock).voidMethod();

(edit: use doNothing, as mentioned by @Rogério)

Issue was due to the jar conflicts

We need to exclude

<dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
        <exclusions>
            <exclusion>
                <groupId>org.junit</groupId>
                <artifactId>junit</artifactId>
            </exclusion>
            <exclusion>
                <groupId>org.mockito</groupId>
                <artifactId>mockito-core</artifactId>
            </exclusion>
            <exclusion>
                <groupId>org.mockito</groupId>
                <artifactId>mockito-all</artifactId>
            </exclusion>
        </exclusions>
    </dependency>

And include

<dependency>
        <groupId>org.mockito</groupId>
        <artifactId>mockito-core</artifactId>
        <version>3.11.2</version>
    </dependency>

You need to create an expectation on jdbcConnection.createStatement().

By default, I believe a null is returned.

Should read something like:

ResultSet resultSet = Mockito.mock(ResultSet.class);
Mockito.when(resultSet.next()).thenReturn(true).thenReturn(true).thenReturn(true).thenReturn(false);
Mockito.when(resultSet.getString(1)).thenReturn("table_r3").thenReturn("table_r1").thenReturn("table_r2");

Statement statement = Mockito.mock(Statement.class);
Mockito.when(statement.executeQuery("SELECT name FROM tables")).thenReturn(resultSet);

Connection jdbcConnection = Mockito.mock(Connection.class);
Mockito.when(jdbcConnection.createStatement()).thenReturn(statement);

You could simply put the thread to sleep for the desired time. Watch out tho - such things can really slow down your automated test execution, so you might want to isolate such tests in a separate suite

It would look similar to this:

when(mock.load("a")).thenAnswer(new Answer<String>() {
   @Override
   public String answer(InvocationOnMock invocation){
     Thread.sleep(5000);
     return "ABCD1234";
   }
});

when(myObject.someMethod()).thenReturn(someMockObject);
// run test
verify(myObject, times(n)).someMethod();

See the documentation for more conversion examples.

First thing, you should be passing spy in as the constructor argument.

That aside, here's how you could do it.

public class ResultCaptor<T> implements Answer {
    private T result = null;
    public T getResult() {
        return result;
    }

    @Override
    public T answer(InvocationOnMock invocationOnMock) throws Throwable {
        result = (T) invocationOnMock.callRealMethod();
        return result;
    }
}

Intended usage:

RealFactory factory     = new RealFactory();
RealFactory spy         = spy(factory);
TestedClass testedClass = new TestedClass(spy);

// At this point I would like to get a reference to the object created
// and returned by the factory.


// let's capture the return values from spy.create()
ResultCaptor<RealThing> resultCaptor = new ResultCaptor<>();
doAnswer(resultCaptor).when(spy).create();

// do something that will trigger a call to the factory
testedClass.doSomething();

// validate the return object
assertThat(resultCaptor.getResult())
        .isNotNull()
        .isInstanceOf(RealThing.class);

You can mock it using PowerMock in combination with Mockito:

On top of your class:

@RunWith(PowerMockRunner.class)
@PrepareForTest({ClassThatCallsTheCalendar.class})

The key to success is that you have to put the class where you use Calendar in PrepareForTest instead of Calendar itself because it is a system class. (I personally had to search a lot before I found this)

Then the mocking itself:

mockStatic(Calendar.class);
when(Calendar.getInstance()).thenReturn(calendar);

You can absolutely inject mocks on MyLauncher in your test. I am sure if you show what mocking framework you are using someone would be quick to provide an answer. With mockito I would look into using @RunWith(MockitoJUnitRunner.class) and using annotations for myLauncher. It would look something like what is below.

@RunWith(MockitoJUnitRunner.class)
public class MyLauncherTest
    @InjectMocks
    private MyLauncher myLauncher = new MyLauncher();

    @Mock
    private MyService myService;

    @Test
    public void someTest() {

    }
}