List of Classes and Methods of org.mockitoinline package of Mockito Framework

It should be something like

@RunWith(SpringJUnit4ClassRunner.class)
public class aTest () {

    @Mock
    private B b;

    @Mock
    private C c;

    @Autowired
    @InjectMocks
    private A a;

}

If you want D to be Autowired dont need to do anything in your Test class. Your Autowired A should have correct instance of D. Also i think you need to use SpringJUnit4ClassRunner for Autowiring to work, with contextConfiguration set correctly. Because you are not using MockitoJunitRunner you need to initialize your mocks yourself using

MockitoAnnotations.initMocks(java.lang.Object testClass)

when(
  fooDao.getBar(
    any(Bazoo.class)
  )
).thenReturn(myFoo);

or (to avoid nulls):

when(
  fooDao.getBar(
    (Bazoo)notNull()
  )
).thenReturn(myFoo);

Don't forget to import matchers (many others are available):

For Mockito 2.1.0 and newer:

import static org.mockito.ArgumentMatchers.*;

For older versions:

import static org.mockito.Matchers.*;

By default, Maven assumes you wrote your code using JDK 1.5 and that you want to compile to that same target. You will need to add the maven-compiler-plugin to your build plugins, in order to tell it to use 1.8.

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.3</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
        </plugin>
    </plugins>
</build>

Check out the plugin's docs for more info: http://maven.apache.org/plugins/maven-compiler-plugin/compile-mojo.html

You can use PowerMockito

See the example:

Second second = Mockito.mock(Second.class);
whenNew(Second.class).withNoArguments().thenReturn(second);

But re-factoring is better decision.

Mocking the iterator works for me. See below code sample:

import static org.junit.Assert.assertEquals;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

import java.util.Collection;
import java.util.Iterator;

import org.junit.Before;
import org.junit.Test;

public class TestMockedIterator {

    private Collection<String> fruits;
    private Iterator<String> fruitIterator;

    @SuppressWarnings("unchecked")
    @Before
    public void setUp() {
        fruitIterator = mock(Iterator.class);
        when(fruitIterator.hasNext()).thenReturn(true, true, true, false);
            when(fruitIterator.next()).thenReturn("Apple")
            .thenReturn("Banana").thenReturn("Pear");

        fruits = mock(Collection.class);
        when(fruits.iterator()).thenReturn(fruitIterator);
    }

    @Test
    public void test() {
        int iterations = 0;
        for (String fruit : fruits) {
            iterations++;
        }
        assertEquals(3, iterations);
    }
}

You need to annotate ProductService with @InjectMocks:

@Autowired
@InjectMocks
private ProductService productService;

This will inject the ClientService mock into your ProductService.

JUnit creates a new instance of test class each time it runs a new test method and runs @Before method each time it creates a new test class. You can easily test it:

@Before
public void setup() {
    System.out.println("setup");
    when(myMock.myMethod()).thenReturn("hello");
}

And MockitoJUnitRunner will create a new MyMock mock instance for every test method.

If the contract of class A includes the fact that it calls method B of an object of type C, then you should test this by making a mock of type C, and verifying that method B has been called.

This implies that the contract of class A has sufficient detail that it talks about type C (which might be an interface or a class). So yes, we're talking about a level of specification that goes beyond just "system requirements", and goes some way to describing implementation.

This is normal for unit tests. When you are unit testing, you want to ensure that each unit is doing the "right thing", and that will usually include its interactions with other units. "Units" here might mean classes, or larger subsets of your application.

Update:

I feel that this doesn't apply just to verification, but to stubbing as well. As soon as you stub a method of a collaborator class, your unit test has become, in some sense, dependent on implementation. It's kind of in the nature of unit tests to be so. Since Mockito is as much about stubbing as it is about verification, the fact that you're using Mockito at all implies that you're going to run across this kind of dependency.

In my experience, if I change the implementation of a class, I often have to change the implementation of its unit tests to match. Typically, though, I won't have to change the inventory of what unit tests there are for the class; unless of course, the reason for the change was the existence of a condition that I failed to test earlier.

So this is what unit tests are about. A test that doesn't suffer from this kind of dependency on the way collaborator classes are used is really a sub-system test or an integration test. Of course, these are frequently written with JUnit too, and frequently involve the use of mocking. In my opinion, "JUnit" is a terrible name, for a product that lets us produce all different types of test.

The easiest way is using Lombok library.

@Value
@Builder
public class MessageEvent<T> {
    T message;
    TypeEnum type;
}

And the usage is like this.

MessageEvent<String> messageEvent = MessageEvent.<String>builder().message("test").build();