How to use should_print_captor_matcher method of org.mockitousage.matchers.CustomMatcherDoesYieldCCETest class

PowerMock is another mock framework that extends EasyMock and Mockito. With PowerMock you can easily remove unwanted behavior from a class, for example a static initializer. In your example you simply add the following annotations to your JUnit test case:

@RunWith(PowerMockRunner.class)
@SuppressStaticInitializationFor("some.package.ClassWithStaticInit")

PowerMock does not use a Java agent and therefore does not require modification of the JVM startup parameters. You simple add the jar file and the above annotations.

Make sure you have the following dependency in your pom file

        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-core</artifactId>
            <version>3.5.15</version>
            <scope>test</scope>
        </dependency>

Use the doReturn-when alternate stubbing syntax.

System under test:

public class MyClass {
  Set<? extends Number> getSet() {
    return new HashSet<Integer>();
  }
}

and the test case:

import static org.mockito.Mockito.*;

import java.util.HashSet;
import java.util.Set;

import org.junit.Test;

public class TestMyClass {
  @Test
  public void testGetSet() {
    final MyClass mockInstance = mock(MyClass.class);

    final Set<Integer> resultSet = new HashSet<Integer>();
    resultSet.add(1);
    resultSet.add(2);
    resultSet.add(3);

    doReturn(resultSet).when(mockInstance).getSet();

    System.out.println(mockInstance.getSet());
  }
}

No errors or warning suppression needed

The problem is the String class in Java is marked as final, so you cannot mock is using traditional mocking frameworks. According to the Mockito FAQ, this is a limitation of that framework as well.

Testing your code is not trivial, though not impossible. My first idea was to use ArgumentCaptor, which is much easier both to use and comprehend compared to ArgumentMatcher. Unfortunately the test still fails - reasons are certainly beyond the scope of this answer, but I may help if that interests you. Still I find this test case interesting enough to be shown (not correct solution):

@RunWith(MockitoJUnitRunner.class)
public class MessageServiceTest {

    @Mock
    private MessageDAO messageDAO = mock(MessageDAO.class);

    private MessageService messageService = new MessageService();

    @Before
    public void setup() {
        messageService.setDao(messageDAO);
    }

    @Test
    public void testAcceptFromOffice() throws Exception {
        //given
        final Message message = new Message();

        //when
        messageService.acceptFromOffice(message);

        //then
        ArgumentCaptor<Message> captor = ArgumentCaptor.forClass(Message.class);

        verify(messageDAO, times(2)).makePersistent(captor.capture());

        final List<Message> params = captor.getAllValues();
        assertThat(params).containsExactly(message, message);

        assertThat(params.get(0).getStatus()).isEqualTo(0);
        assertThat(params.get(1).getStatus()).isEqualTo(1);
    }

}

Unfortunately the working solution requires somewhat complicated use of Answer. In a nutshell, instead of letting Mockito to record and verify each invocation, you are providing sort of callback method that is executed every time your test code executes given mock. In this callback method (MakePersistentCallback object in our example) you have access both to parameters and you can alter return value. This is a heavy cannon and you should use it with care:

    @Test
    public void testAcceptFromOffice2() throws Exception {
        //given
        final Message message = new Message();
        doAnswer(new MakePersistentCallback()).when(messageDAO).makePersistent(message);

        //when
        messageService.acceptFromOffice(message);

        //then
        verify(messageDAO, times(2)).makePersistent(message);
    }


    private static class MakePersistentCallback implements Answer {

        private int[] expectedStatuses = {0, 1};
        private int invocationNo;

        @Override
        public Object answer(InvocationOnMock invocation) throws Throwable {
            final Message actual = (Message)invocation.getArguments()[0];
            assertThat(actual.getStatus()).isEqualTo(expectedStatuses[invocationNo++]);
            return null;
        }
    }

The example is not complete, but now the test succeeds and, more importantly, fails when you change almost anything in CUT. As you can see MakePersistentCallback.answer method is called every time mocked messageService.acceptFromOffice(message) is called. Inside naswer you can perform all the verifications you want.

NB: Use with caution, maintaining such tests can be troublesome to say the least.

Property injection is like that is not so easy to test. In this case, Constructor injection is much better. Refactor your constructor to look like this:

private final RssService rssService;

@Inject
public RssListPresenter(RssService rssService) {
        this.rssService = rssService;
}

Now you can test it easily:

//mocks
RssService mockRssService;

//system under test
RssListPresenter rssListPresenter;

@Before
public void setup() {
    mockRssService = Mockito.mock(RssService.class);
    rssListPresenter = new RssListPresenter(mockRssService);
}

You probably shouldn't be using DaggerNetworkComponent.inject(this) inside RssListPresenter. Instead you should be configuring dagger so that when it injects members into your top-level classes (Activity, Fragment, Service) it can access the object graph and create an instance of your RssPresenter.

Why only put injectors in Activity and Service and not in something like RssListPresenter? These are classes that are instantiated by the Android system and so you have no choice but to use injectors.

To clarify, Activity, Fragment etc. are ideal injection targets. RssListPresenter etc. are injected dependencies. You need to configure the dependency injection framework, dagger, so that it can provide the correct dependencies to inject into the injection targets.

So you will also need to write a @Provides method for RssListPresenter

@Provides provideRssListPresenter(RssService rssService) {
    return new RssListPresenteR(rssService);
}

In Mockito 2.1.0 and up with Java 8 you can pass the lambda to argThat out of the box so that one does not need a custom argument matchers. For the example in the OP would be:

verify(mockedFoo).doThing(argThat((Bar aBar) -> aBar.getI() == 5));

This is because as of Mockito 2.1.0, ArgumentMatcher is a functional interface.

The right thing to do is to restructure your code to make it more testable as shown below. Restructuring your code to remove the direct dependency on Date will allow you to inject different implementations for normal runtime and test runtime:

interface DateTime {
    Date getDate();
}

class DateTimeImpl implements DateTime {
    @Override
    public Date getDate() {
       return new Date();
    }
}

class MyClass {

    private final DateTime dateTime;
    // inject your Mock DateTime when testing other wise inject DateTimeImpl

    public MyClass(final DateTime dateTime) {
        this.dateTime = dateTime;
    }

    public long getDoubleTime(){
        return dateTime.getDate().getTime()*2;
    }
}

public class MyClassTest {
    private MyClass myClassTest;

    @Before
    public void setUp() {
        final Date date = Mockito.mock(Date.class);
        Mockito.when(date.getTime()).thenReturn(30L);

        final DateTime dt = Mockito.mock(DateTime.class);
        Mockito.when(dt.getDate()).thenReturn(date);

        myClassTest = new MyClass(dt);
    }

    @Test
    public void someTest() {
        final long doubleTime = myClassTest.getDoubleTime();
        assertEquals(60, doubleTime);
    }
}

An alternative to ArgumentMatcher is ArgumentCaptor.

Official example:

ArgumentCaptor<Person> argument = ArgumentCaptor.forClass(Person.class);
verify(mock).doSomething(argument.capture());
assertEquals("John", argument.getValue().getName());

A captor can also be defined using the @Captor annotation:

@Captor ArgumentCaptor<Person> captor;
//... MockitoAnnotations.initMocks(this);
@Test public void test() {
    //...
    verify(mock).doSomething(captor.capture());
    assertEquals("John", captor.getValue().getName());
}