Usages of doThrow doAnswer doNothing and doReturn in mockito

Question

I was learning mockito and I understood the basic usages of the above mentioned functions from the link   But I would like to know whether it can be used for any other cases

User · Answer

If you are testing a logic class and it is calling some internal void methods the doNothing is perfect

User · Answer

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 lt ReturnValueObject gt                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  Is the easiest of the list  basically it tells Mockito to do nothing when a method in a mock object is called  Sometimes used in void return methods or method that does not have side effects  or are not related to the unit testing you are doing   public void updateRequestActionAndApproval final List lt Object1 gt  cmItems    Mockito doNothing   when pagLogService  updateRequestActionAndApproval                  Matchers any Object1 class

User · Answer

To add a bit to accepted answer     If you get an UnfinishedStubbingException  be sure to set the method to be stubbed after the when closure  which is different than when you write Mockito when Mockito doNothing   when mock  method        method is declared after  when  closes  Mockito when mock method    thenReturn something      method is declared inside  when

User · Answer

A very simple example is that if you have a UserService that has  Autowired jpa resposiroty UserRepository       class UserService      Autowired   UserRepository userRepository          then in the test class for UserService you will do       class TestUserService     Mock    UserRepository userRepository      InjectMocks   UserService userService            InjectMocks tells the framework that take the  Mock UserRepository userRespository  and inject that into userService so rather than auto wiring a real instance of UserRepository a Mock of UserRepository will be injected in userService

User · Answer

It depends on the kind of test double you want to interact with    If you don t use doNothing and you mock an object  the real method is not called If you don t use doNothing and you spy an object  the real method is called   In other words  with mocking the only useful interactions with a collaborator are the ones that you provide  By default functions will return null  void methods do nothing

[java] Usages of doThrow() doAnswer() doNothing() and doReturn() in mockito

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