Using Mockito with multiple calls to the same method with the same arguments

Question

Is there a way to have a stubbed method return different objects on subsequent invocations? I'd like to do this to test nondeterminate responses from an ExecutorCompletionService. i.e. to test that irrespective of the return order of the methods, the outcome remains constant.

The code I'm looking to test looks something like this.

// Create an completion service so we can group these tasks together
ExecutorCompletionService<T> completionService =
        new ExecutorCompletionService<T>(service);

// Add all these tasks to the completion service
for (Callable<T> t : ts)
    completionService.submit(request);

// As an when each call finished, add it to the response set.
for (int i = 0; i < calls.size(); i ++) {
    try {
        T t = completionService.take().get();
        // do some stuff that I want to test
    } catch (...) { }        
}

score 923 · Answer 1 · answered Dec 06 '11 at 05:21

923

How about

when( method-call ).thenReturn( value1, value2, value3 );

You can put as many arguments as you like in the brackets of thenReturn, provided they're all the correct type. The first value will be returned the first time the method is called, then the second answer, and so on. The last value will be returned repeatedly once all the other values are used up.

answered Dec 06 '11 at 05:21

Dawood ibn Kareem

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This will work with a mock, but not with a spy. If you need to prevent calling the original method you need doAnswer(...).when(someSpy).someMethod(...). – Yuri Dec 11 '14 at 00:01
7

@Yuri - not quite. You don't need `doAnswer` or to write an `Answer` in the case that you mention. You can just use `doReturn(...).when(someSpy).someMethod(...)`. It seems reasonable to assume that Emma is interested in mocks, rather than spies, but I guess I could add something to my answer to spell this out. Thanks for the comment. – Dawood ibn Kareem Dec 11 '14 at 00:06
@DawoodibnKareem lets say for the first call I want to return a value and for the second call I want to throw an Exception. How can this be done? – Rito Sep 11 '17 at 12:18
@Rito Please read Volodymyr's answer or Raystorm's answer. They both cover that case. – Dawood ibn Kareem Sep 11 '17 at 18:18
Wow, have wasted almost 3 hours debugging HashSet, Spring beans...others, in a loop of 3, thenReturn was giving the same mock object, which results in same hashCode in HashSet, which results in HashSet having 1 element instead of 3 elements, which results in test case failures due to assertion. Thanks. – Yoga Gowda Oct 05 '19 at 19:22
"Thank You" I really want to stress "thank you" again:D – Joker Jul 10 '20 at 11:01
Thanks! Works with different kinds of answers as well: `when(foo).thenThrow(new RuntimeException(), new RuntimeException().thenReturn(null);` – Dimitrios K. May 28 '21 at 14:10

score 343 · Accepted Answer · edited Oct 10 '17 at 07:03

343

You can do that using the thenAnswer method (when chaining with when):

when(someMock.someMethod()).thenAnswer(new Answer() {
    private int count = 0;

    public Object answer(InvocationOnMock invocation) {
        if (count++ == 1)
            return 1;

        return 2;
    }
});

Or using the equivalent, static doAnswer method:

doAnswer(new Answer() {
    private int count = 0;

    public Object answer(InvocationOnMock invocation) {
        if (count++ == 1)
            return 1;

        return 2;
    }
}).when(someMock).someMethod();

edited Oct 10 '17 at 07:03

nbrooks

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answered Nov 11 '11 at 00:21

Igor Nikolaev

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This answer helped me a lot because `doAnswer()`/`thenAnswer()` do not allow chaining multiple calls as `doReturn()`/`thenReturn()` do and I needed to compute something and not just return a different value. Creating an anonymous `Answer` object with a private `count` variable was what did the trick for me. – Lucio Paiva Aug 20 '20 at 18:19
Keep in mind that these are not equivalent when `someMethod()` returns `void`. See [this](https://stackoverflow.com/questions/2276271/how-to-mock-void-methods-with-mockito) answer for more details. – Raphael Nov 18 '20 at 23:17
Works as a charm. – Juliano Suman Curti Nov 17 '22 at 15:57
@LucioPaiva Where do you get the information, that you can not chain "doAnswer" calls with other calls? Is this a known bug, feature or something else? – KFleischer Jun 12 '23 at 08:59

score 234 · Answer 3 · edited May 23 '17 at 12:34

234

As previously pointed out almost all of the calls are chainable.

So you could call

when(mock.method()).thenReturn(foo).thenReturn(bar).thenThrow(new Exception("test"));

//OR if you're mocking a void method and/or using spy instead of mock

doReturn(foo).doReturn(bar).doThrow(new Exception("Test").when(mock).method();

More info in Mockito's Documenation.

edited May 23 '17 at 12:34

Community

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answered Nov 13 '15 at 17:35

Raystorm

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Very helpful! What would happen the 4th time `mock.method` was called in this example? I want something like, return foo the first time but return bar for ALL the rest. – javaPlease42 Jan 20 '16 at 21:52
7

Each additional invocation on the mock will return the last 'thenReturn' or the last 'thenThrow' Very useful – Francois Lacoursiere Jan 22 '16 at 21:48
Thank you for the great and simple instructions. Never knew this until now. I was struggling to find how to get back two different results on two identical call. Save me tons of time. – CharlesC Sep 26 '19 at 14:45
Excellent solution! Using this. – lance-java Feb 12 '21 at 16:42

Volodymyr Kozubal · Answer 4 · 2021-10-13T02:03:02.377

89

Almost all of the calls are chainable:

doReturn(null).doReturn(anotherInstance).when(mock).method();

edited Oct 13 '21 at 02:03

answered May 13 '15 at 15:13

Volodymyr Kozubal

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epox · Answer 5 · 2023-06-19T21:37:28.147

BDD style:

import static org.mockito.BDDMockito.given;
        ...

        given(yourMock.yourMethod()).willReturn(1, 2, 3);

Classic style:

import static org.mockito.Mockito.when;
        ...

        when(yourMock.yourMethod()).thenReturn(1, 2, 3);

Explicit style:

        ...

        when(yourMock.yourMethod())
            .thenReturn(1)
            .thenReturn(2)
            .thenReturn(3);

Depending on an arg

Option #1

Suppose we have 2 args, and check the size of the 2nd (list) arg:

        ...

        when(yourMock.yourMethod(any(), anyList()))
             .thenAnswer(args -> ((List) args.getArgument(1)).size() < 2
                                 ? 1
                                 : 3);

args are Objects, so we have to cast an arg to our type. I cast ^^^ to (List) in my case.

Option #2 (BDD)

        ...

        given(yourMock.yourMethod(any(), anyList()))
             .willAnswer(args -> ((List) args.getArgument(1)).size() < 2
                                 ? 1
                                 : 3);

score 5 · Answer 6 · edited Jun 23 '16 at 11:48

5

I've implemented a MultipleAnswer class that helps me to stub different answers in every call. Here the piece of code:

private final class MultipleAnswer<T> implements Answer<T> {

    private final ArrayList<Answer<T>> mAnswers;

    MultipleAnswer(Answer<T>... answer) {
        mAnswers = new ArrayList<>();
        mAnswers.addAll(Arrays.asList(answer));
    }

    @Override
    public T answer(InvocationOnMock invocation) throws Throwable {
        return mAnswers.remove(0).answer(invocation);
    }
}

edited Jun 23 '16 at 11:48

mnille

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answered Jun 23 '16 at 11:03

victorvmp

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Can you initialize that object in a short, simple and readable way? – usr-local-ΕΨΗΕΛΩΝ Sep 27 '18 at 14:03

score 4 · Answer 7 · answered Feb 09 '20 at 17:35

4

doReturn( value1, value2, value3 ).when( method-call )

answered Feb 09 '20 at 17:35

enhancedJack

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Do you mean `doReturn(value1, value2, value3).when(mock).methodCall()` perhaps? – Dawood ibn Kareem Jul 15 '20 at 01:22

score 3 · Answer 8 · answered Jan 11 '19 at 19:44

Related to @[Igor Nikolaev]'s answer from 8 years ago, using an Answer can be simplified somewhat using a lambda expression available in Java 8.

when(someMock.someMethod()).thenAnswer(invocation -> {
    doStuff();
    return;
});

or more simply:

when(someMock.someMethod()).thenAnswer(invocation -> doStuff());

score 2 · Answer 9 · answered Sep 23 '21 at 16:10

This is not directly related to the question. But wanted to put this in the same chain.

If trying to verify the same method call with multiple arguments, you can use the below times feature by Mockito. You don't need it if you are not verifying.

Mockito.verify(method, times(n)).methoscall();

Here is 'n' is the number of times the mock is invoked.

score 2 · Answer 10 · answered Nov 24 '21 at 12:19

2

If you have a dynamic list of values you can use AdditionalAnswers.returnsElementsOf:

import org.mockito.AdditionalAnswers;

when(mock.method()).thenAnswer(AdditionalAnswers.returnsElementsOf(myListOfValues));

answered Nov 24 '21 at 12:19

Florent M.

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score 1 · Answer 11 · answered Jun 23 '16 at 08:06

Following can be used as a common method to return different arguments on different method calls. Only thing we need to do is we need to pass an array with order in which objects should be retrieved in each call.

@SafeVarargs
public static <Mock> Answer<Mock> getAnswerForSubsequentCalls(final Mock... mockArr) {
    return new Answer<Mock>() {
       private int count=0, size=mockArr.length;
       public Mock answer(InvocationOnMock invocation) throws throwable {
           Mock mock = null;
           for(; count<size && mock==null; count++){
                mock = mockArr[count];
           }

           return mock;    
       } 
    }
}

Ex. getAnswerForSubsequentCalls(mock1, mock3, mock2); will return mock1 object on first call, mock3 object on second call and mock2 object on third call. Should be used like when(something()).doAnswer(getAnswerForSubsequentCalls(mock1, mock3, mock2)); This is almost similar to when(something()).thenReturn(mock1, mock3, mock2);

score 1 · Answer 12 · answered Feb 12 '21 at 16:47

1

You can use a LinkedList and an Answer. Eg

MyService mock = mock(MyService.class);
LinkedList<String> results = new LinkedList<>(List.of("A", "B", "C"));
when(mock.doSomething(any())).thenAnswer(invocation -> results.removeFirst());

answered Feb 12 '21 at 16:47

lance-java

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score 1 · Answer 13 · answered Dec 07 '21 at 08:24

This might be basic/obvious, but if like me you are trying to mock multiple calls for a method that is called unknown number of times per call to method to be tested, for example:

public String method(String testArg) {
    //...
    while(condition) {
        someValue = someBean.nestedMethod(); // This is called unknown number of times
        //...
    }
    //...
}

You can do something like:

@Test
public void testMethod() {
    mockNestedMethodForValue("value1");
    assertEquals(method("arg"), "expected1");
    mockNestedMethodForValue("value2");
    assertEquals(method("arg"), "expected2");
    mockNestedMethodForValue("value3");
    assertEquals(method("arg"), "expected3");
}

private void mockNestedMethodForValue(String value) {
    doReturn(value).when(someBeanMock).nestedMethod();
}

score 0 · Answer 14 · answered Dec 04 '20 at 07:56

0

Here is working example in BDD style which is pretty simple and clear

given(carRepository.findByName(any(String.class))).willReturn(Optional.empty()).willReturn(Optional.of(MockData.createCarEntity()));

answered Dec 04 '20 at 07:56

Tsvetoslav Tsvetkov

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Using Mockito with multiple calls to the same method with the same arguments

14 Answers14

BDD style:

Classic style:

Explicit style:

Depending on an arg

Linked

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