How to use should_keep_same_instance_if_field_initialized method of org.mockito.internal.util.reflection.FieldInitializerTest class

Since Mockito 1.9.5+ and Java 8+

You can use a lambda expression, like:

when(myMock.myFunction(anyString())).thenAnswer(i -> i.getArguments()[0]);

Where i is an instance of InvocationOnMock.

For older versions

You can create an Answer in Mockito. Let's assume, we have an interface named MyInterface with a method myFunction.

public interface MyInterface {
    public String myFunction(String abc);
}

Here is the test method with a Mockito answer:

public void testMyFunction() throws Exception {
    MyInterface mock = mock(MyInterface.class);
    when(mock.myFunction(anyString())).thenAnswer(new Answer<String>() {
    @Override
    public String answer(InvocationOnMock invocation) throws Throwable {
        Object[] args = invocation.getArguments();
        return (String) args[0];
    }
    });

    assertEquals("someString",mock.myFunction("someString"));
    assertEquals("anotherString",mock.myFunction("anotherString"));
}

You're surprised that the writes on the new objects aren't writing through to the backing collection?

Collections.transform doesn't just do the transform "as needed" -- it doesn't store anything at all. That's what "view" means in its documentation. Any time you walk through a Collections2.transformed collection, it applies the function again, freshly. Once that for loop in the apply method is done with result, that object is gone; never seen again.

If you want to do what you're doing, make an explicit copy of the transformed collection in e.g. an ArrayList.

Try to use Mockito or Easymock for mocking service calls. You need to mock only these methods which are actually used - no need to mock every method. You can creat mock object for WebResource class, then mock accept method call.

In @BeforeClass/@Before JUnit test method write something like (Mockito example)

WebResource res = mock(WebResource.class);
when(res.accept(something)).thenReturn(thatWhatYouWant);

Then in your tests you can use res object as if it was real object and call mock method on it. Instead of returning value you can also throw exceptions. Mockito is pretty cool.

doThrow : Basically used when you want to throw an exception when a method is being called within a mock object.

public void validateEntity(final Object object){}
Mockito.doThrow(IllegalArgumentException.class)
.when(validationService).validateEntity(Matchers.any(AnyObjectClass.class));

doReturn : Used when you want to send back a return value when a method is executed.

public Socket getCosmosSocket() throws IOException {}
Mockito.doReturn(cosmosSocket).when(cosmosServiceImpl).getCosmosSocket();

doAnswer: Sometimes you need to do some actions with the arguments that are passed to the method, for example, add some values, make some calculations or even modify them doAnswer gives you the Answer<?> interface that being executed in the moment that method is called, this interface allows you to interact with the parameters via the InvocationOnMock argument. Also, the return value of answer method will be the return value of the mocked method.

public ReturnValueObject quickChange(Object1 object);
Mockito.doAnswer(new Answer<ReturnValueObject>() {

        @Override
        public ReturnValueObject answer(final InvocationOnMock invocation) throws Throwable {

            final Object1 originalArgument = (invocation.getArguments())[0];
            final ReturnValueObject returnedValue = new ReturnValueObject();
            returnedValue.setCost(new Cost());

            return returnedValue ;
        }
}).when(priceChangeRequestService).quickCharge(Matchers.any(Object1.class));

doNothing: (From documentation) Use doNothing() for setting void methods to do nothing. Beware that void methods on mocks do nothing by default! However, there are rare situations when doNothing() comes handy:

• Stubbing consecutive calls on a void method:

  doNothing().
  doThrow(new RuntimeException())
  .when(mock).someVoidMethod();
  
  //does nothing the first time:
  mock.someVoidMethod();
  
  //throws RuntimeException the next time:
  mock.someVoidMethod();
  

• When you spy real objects and you want the void method to do nothing:

  List list = new LinkedList();
  List spy = spy(list);
  
  //let's make clear() do nothing
  doNothing().when(spy).clear();
  
  spy.add("one");
  
  //clear() does nothing, so the list still contains "one"
  spy.clear();
  

• any() checks absolutely nothing. Since Mockito 2.0, any(T.class) shares isA semantics to mean "any T" or properly "any instance of type T".

  This is a change compared to Mockito 1.x, where any(T.class) checked absolutely nothing but saved a cast prior to Java 8: "Any kind object, not necessary of the given class. The class argument is provided only to avoid casting."

• isA(T.class) checks that the argument instanceof T, implying it is non-null.

• same(obj) checks that the argument refers to the same instance as obj, such that arg == obj is true.

• eq(obj) checks that the argument equals obj according to its equals method. This is also the behavior if you pass in real values without using matchers.

  Note that unless equals is overridden, you'll see the default Object.equals implementation, which would have the same behavior as same(obj).

If you need more exact customization, you can use an adapter for your own predicate:

• For Mockito 1.x, use argThat with a custom Hamcrest Matcher<T> that selects exactly the objects you need.
• For Mockito 2.0 and beyond, use Matchers.argThat with a custom org.mockito.ArgumentMatcher<T>, or MockitoHamcrest.argThat with a custom Hamcrest Matcher<T>.

You may also use refEq, which uses reflection to confirm object equality; Hamcrest has a similar implementation with SamePropertyValuesAs for public bean-style properties. Note that on GitHub issue #1800 proposes deprecating and removing refEq, and as in that issue you might prefer eq to better give your classes better encapsulation over their sense of equality.

The following, running under Mockito 1.9.0 and JUnit 4.8.2, does not print anything to my console:

import static org.mockito.Mockito.*;

import org.junit.Test;

public class TestNonCall {
  public class TestClass {
    public String test() {
      System.out.println("test called!");
      return "test";
    }
  }

  @Test
  public void doTest() {
    final TestClass mock = mock(TestClass.class);

    when(mock.test()).thenReturn("mock!");
  }
}

Further, if I put a breakpoint in the test() method it is never hit.

Perhaps post more code? It looks like your example is not complex enough to demonstrate the behaviour you're having problems with.

Also: are you using the latest version of Mockito?

Edit: New Thought: Are You Mocking a Final Method?

If you add a final modifier to the method you are mocking, you get the behaviour you reported.

This is because Mockito does not mock final and static methods. Instead, it delegates the calls to the real implementation.

Might your actual code be attempting to mock a final method?

If so, you can use PowerMock, which is an extension to Mockito that allows mocking final methods.

You would need to add the following annotations to your test case class:

@RunWith(PowerMockRunner.class)
@PrepareForTest(TestClass.class)
public class TestNonCall {
  // ...
}

and mock the class using the PowerMock method in your test method:

final TestClass mock = PowerMockito.mock(TestClass.class);

then proceed as usual.

I wanted to do the same thing, and eventually accomplished it by using the Mockito "spy" function, which wraps a real object with a mock object. All calls to the mock object get forwarded to the real object, except those you are trying to mock. For example:

ObjectMapper om = Mockito.spy(new ObjectMapper());
Mockito.when( om.writeValueAsString(ErrorObject.class)).thenThrow(new JsonProcessingException("") {});

All usages of om will be handled by the underlying ObjectMapper instance until an instance of ErrorObject gets passed in, at which point the JsonProcessingException will be thrown.

The newJsonProcessingException is created as an anonymous class, as it is a protected class and only a sub-class can be instantiated.

PowerMock 1.6 isn't compatible with Mockito 2.7 (take a look at https://github.com/powermock/powermock/wiki/Mockito#supported-versions)

You should use PowerMock 1.7.0RC2 (or 1.7.0RC3 if 1.7.0RC2 doesn't work), and also use powermock-api-mockito2 instead of powermock-api-mockito.

Try the anyVararg() matcher. This was introduced in 1.8.1.