Mockito - difference between doReturn and when

Question

I am currently in the process of using Mockito to mock my service layer objects in a Spring MVC application in which I want to test my Controller methods  However  as I have been reading on the specifics of Mockito  I have found that the methods doReturn      when      is equivalent to when      thenReturn       So  my question is what is the point of having two methods that do the same thing or what is the subtle difference between doReturn      when      and when      thenReturn        Any help would be appreciated

User · Answer

Continuing this answer  There is another difference that if you want your method to return different values for example when it is first time called  second time called etc then you can pass values so for example     PowerMockito doReturn false  false  true  when SomeClass class   SomeMethod   Matchers any SomeClass class      So it will return false when the method is called in same test case and then it will return false again and lastly true

User · Answer

The latter alternative is used for methods on mocks that return void   Please have a look  for example  here  How to make mock to void methods with mockito

User · Answer

The two syntaxes for stubbing are roughly equivalent   However  you can always use doReturn when for stubbing  but there are cases where you can t use when thenReturn   Stubbing void methods is one such   Others include use with Mockito spies  and stubbing the same method more than once   One thing that when thenReturn gives you  that doReturn when doesn t  is type-checking of the value that you re returning  at compile time   However  I believe this is of almost no value - if you ve got the type wrong  you ll find out as soon as you run your test   I strongly recommend only using doReturn when   There is no point in learning two syntaxes when one will do   You may wish to refer to my answer at Forming Mockito  quot grammars quot  - a more detailed answer to a very closely related question

User · Answer

The Mockito javadoc seems to tell why use doReturn   instead of when   Use doReturn   in those rare occasions when you cannot use Mockito when Object        Beware that Mockito when Object  is always recommended for stubbing   because it is argument type-safe and more readable  especially when   stubbing consecutive calls         Here are those rare occasions when doReturn   comes handy        1  When spying real objects and calling real methods on a spy brings side   effects       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        2  Overriding a previous exception-stubbing       when mock foo    thenThrow new RuntimeException            Impossible  the exception-stubbed foo   method is called so   RuntimeException is thrown  when mock foo    thenReturn  bar           You have to use doReturn   for stubbing       doReturn  bar   when mock  foo      Above scenarios shows a tradeoff   of Mockito s elegant syntax  Note that the scenarios are very rare    though  Spying should be sporadic and overriding exception-stubbing is   very rare  Not to mention that in general overridding stubbing is a   potential code smell that points out too much stubbing

User · Answer

Both approaches behave differently if you use a spied object  annotated with  Spy  instead of a mock  annotated with  Mock     when      thenReturn      makes a real method call just before the specified value will be returned  So if the called method throws an Exception you have to deal with it   mock it etc  Of course you still get your result  what you define in thenReturn       doReturn      when      does not call the method at all    Example   public class MyClass        protected String methodToBeTested                return anotherMethodInClass                 protected String anotherMethodInClass               throw new NullPointerException               Test    Spy private MyClass myClass              would work fine doReturn  test   when myClass  anotherMethodInClass        would throw a NullPointerException when myClass anotherMethodInClass    thenReturn  test

[java] Mockito - difference between doReturn() and when()

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