Mockito: Trying to spy on method is calling the original method

Let me quote the official documentation:

Important gotcha on spying real objects! Sometimes it's impossible to use when(Object) for stubbing spies. Example: List list = new LinkedList(); List spy = spy(list); // Impossible: real method is called so spy.get(0) throws IndexOutOfBoundsException (the list is yet empty) when(spy.get(0)).thenReturn("foo"); // You have to use doReturn() for stubbing doReturn("foo").when(spy).get(0);

In your case it goes something like:

doReturn(resultsIWant).when(myClassSpy).method1();

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In my case, using Mockito 2.0, I had to change all the any() parameters to nullable() in order to stub the real call.

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My case was different from the accepted answer. I was trying to mock a package-private method for an instance that did not live in that package

package common;

public class Animal {
  void packageProtected();
}

package instances;

class Dog extends Animal { }

and the test classes

package common;

public abstract class AnimalTest<T extends Animal> {
  @Before
  setup(){
    doNothing().when(getInstance()).packageProtected();
  }

  abstract T getInstance();
}

package instances;

class DogTest extends AnimalTest<Dog> {
  Dog getInstance(){
    return spy(new Dog());
  }

  @Test
  public void myTest(){}
}

The compilation is correct, but when it tries to setup the test, it invokes the real method instead.

Declaring the method protected or public fixes the issue, tho it's not a clean solution.

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The answer by Tomasz Nurkiewicz appears not to tell the whole story!

NB Mockito version: 1.10.19.

I am very much a Mockito newb, so can't explain the following behaviour: if there's an expert out there who can improve this answer, please feel free.

The method in question here, getContentStringValue, is NOT final and NOT static.

This line does call the original method getContentStringValue:

doReturn( "dummy" ).when( im ).getContentStringValue( anyInt(), isA( ScoreDoc.class ));

This line does not call the original method getContentStringValue:

doReturn( "dummy" ).when( im ).getContentStringValue( anyInt(), any( ScoreDoc.class ));

For reasons which I can't answer, using isA() causes the intended (?) "do not call method" behaviour of doReturn to fail.

Let's look at the method signatures involved here: they are both static methods of Matchers. Both are said by the Javadoc to return null, which is a little difficult to get your head around in itself. Presumably the Class object passed as the parameter is examined but the result either never calculated or discarded. Given that null can stand for any class and that you are hoping for the mocked method not to be called, couldn't the signatures of isA( ... ) and any( ... ) just return null rather than a generic parameter* <T>?

Anyway:

public static <T> T isA(java.lang.Class<T> clazz)

public static <T> T any(java.lang.Class<T> clazz)

The API documentation does not give any clue about this. It also seems to say the need for such "do not call method" behaviour is "very rare". Personally I use this technique all the time: typically I find that mocking involves a few lines which "set the scene" ... followed by calling a method which then "plays out" the scene in the mock context which you have staged... and while you are setting up the scenery and the props the last thing you want is for the actors to enter stage left and start acting their hearts out...

But this is way beyond my pay grade... I invite explanations from any passing Mockito high priests...

* is "generic parameter" the right term?

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One more possible scenario which may causing issues with spies is when you're testing spring beans (with spring test framework) or some other framework that is proxing your objects during test.

Example

@Autowired
private MonitoringDocumentsRepository repository

void test(){
    repository = Mockito.spy(repository)
    Mockito.doReturn(docs1, docs2)
            .when(repository).findMonitoringDocuments(Mockito.nullable(MonitoringDocumentSearchRequest.class));
}

In above code both Spring and Mockito will try to proxy your MonitoringDocumentsRepository object, but Spring will be first, which will cause real call of findMonitoringDocuments method. If we debug our code just after putting a spy on repository object it will look like this inside debugger:

repository = MonitoringDocumentsRepository$$EnhancerBySpringCGLIB$$MockitoMock$

@SpyBean to the rescue

If instead @Autowired annotation we use @SpyBean annotation, we will solve above problem, the SpyBean annotation will also inject repository object but it will be firstly proxied by Mockito and will look like this inside debugger

repository = MonitoringDocumentsRepository$$MockitoMock$$EnhancerBySpringCGLIB$

and here is the code:

@SpyBean
private MonitoringDocumentsRepository repository

void test(){
    Mockito.doReturn(docs1, docs2)
            .when(repository).findMonitoringDocuments(Mockito.nullable(MonitoringDocumentSearchRequest.class));
}

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Important gotcha on spying real objects

When stubbing a method using spies , please use doReturn() family of methods.

when(Object) would result in calling the actual method that can throw exceptions.

List spy = spy(new LinkedList());

//Incorrect , spy.get() will throw IndexOutOfBoundsException   
 when(spy.get(0)).thenReturn("foo");

//You have to use doReturn() for stubbing    
doReturn("foo").when(spy).get(0);

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I've found yet another reason for spy to call the original method.

Someone had the idea to mock a final class, and found about MockMaker:

As this works differently to our current mechanism and this one has different limitations and as we want to gather experience and user feedback, this feature had to be explicitly activated to be available ; it can be done via the mockito extension mechanism by creating the file src/test/resources/mockito-extensions/org.mockito.plugins.MockMaker containing a single line: mock-maker-inline

Source: https://github.com/mockito/mockito/wiki/What%27s-new-in-Mockito-2#mock-the-unmockable-opt-in-mocking-of-final-classesmethods

After I merged and brought that file to my machine, my tests failed.

I just had to remove the line (or the file), and spy() worked.

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One way to make sure a method from a class is not called is to override the method with a dummy.

    WebFormCreatorActivity activity = spy(new WebFormCreatorActivity(clientFactory) {//spy(new WebFormCreatorActivity(clientFactory));
            @Override
            public void select(TreeItem i) {
                log.debug("SELECT");
            };
        });

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As mentioned in some of the comments, my method was "static" (though being called on by an instance of the class)

public class A {
  static void myMethod() {...}
}
A instance = spy(new A());
verify(instance).myMethod(); // still calls the original method because it's static

Work around was make an instance method or upgrade Mockito to a newer version with some config: https://stackoverflow.com/a/62860455/32453

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Bit late to the party but above solutions did not work for me , so sharing my 0.02$

Mokcito version: 1.10.19

MyClass.java

private int handleAction(List<String> argList, String action)

Test.java

MyClass spy = PowerMockito.spy(new MyClass());

Following did NOT work for me (actual method was being called):

1.

doReturn(0).when(spy , "handleAction", ListUtils.EMPTY_LIST, new String());

2.

doReturn(0).when(spy , "handleAction", any(), anyString());

3.

doReturn(0).when(spy , "handleAction", null, null);

Following WORKED:

doReturn(0).when(spy , "handleAction", any(List.class), anyString());

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