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 lt T gt  completionService           new ExecutorCompletionService lt T gt  service       Add all these tasks to the completion service for  Callable lt T gt  t   ts      completionService submit request       As an when each call finished  add it to the response set  for  int i   0  i  lt  calls size    i           try           T t   completionService take   get               do some stuff that I want to test       catch

User · Answer

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

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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  lt Mock gt  Answer lt Mock gt  getAnswerForSubsequentCalls final Mock    mockArr        return new Answer lt Mock gt             private int count 0  size mockArr length         public Mock answer InvocationOnMock invocation  throws throwable              Mock mock   null             for   count lt size  amp  amp  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

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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

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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

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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

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doReturn  value1  value2  value3   when  method-call

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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 - gt        doStuff        return        or more simply   when someMock someMethod    thenAnswer invocation - gt  doStuff

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You can even chain doReturn   method invocations like this  doReturn null  doReturn anotherInstance  when mock  method      cute isn t it

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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

User · Answer

You can use a LinkedList and an Answer  Eg MyService mock   mock MyService class   LinkedList lt String gt  results   new LinkedList lt  gt  List of  quot A quot    quot B quot    quot C quot     when mock doSomething any     thenAnswer invocation - gt  results removeFirst

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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 lt T gt  implements Answer lt T gt         private final ArrayList lt Answer lt T gt  gt  mAnswers       MultipleAnswer Answer lt T gt     answer            mAnswers   new ArrayList lt  gt             mAnswers addAll Arrays asList answer                Override     public T answer InvocationOnMock invocation  throws Throwable           return mAnswers remove 0  answer invocation

[java] Using Mockito with multiple calls to the same method with the same arguments

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