when I run mockito test occurs WrongTypeOfReturnValue Exception

Question

Error detail   org mockito exceptions misusing WrongTypeOfReturnValue   Boolean cannot be returned by updateItemAttributesByJuId   updateItemAttributesByJuId   should return ResultRich This exception might occur in wrongly written multi-threaded tests  Please refer to Mockito FAQ on limitations of concurrency testing    my code     InjectMocks protected ItemArrangeManager arrangeManagerSpy   spy new ItemArrangeManagerImpl      Mock protected JuItemWriteService juItemWriteService   when arrangeManagerSpy      updateItemAttributes mapCaptor capture    eq juId   eq itemTO getSellerId           thenReturn false     As you can see  I am calling when on updateItemAttributes  which does return a boolean  not on updateItemAttributesByJuId     Why is Mockito attempting to return a boolean from updateItemAttributesByJuId   How can this be rectified

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For me the issue were the multithreaded tests that were doing stubbing/verification on a shared mocks. It leaded to randomly throwing WrongTypeOfReturnValue exception.

This is not properly written test using Mockito. Mocks should not be accessed from multiple threads.

The solution was to make mocks local to each test.

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Error      org mockito exceptions misusing WrongTypeOfReturnValue    String cannot be returned by size     size   should return int         If you re unsure why you re getting above error read on    Due to the nature of the syntax above problem might occur because    1  This exception might occur in wrongly written multi-threaded   tests    Please refer to Mockito FAQ on limitations of concurrency testing    2  A spy is stubbed using when spy foo    then   syntax  It is safer to   stub spies -   - with doReturn Throw   family of methods  More in javadocs for   Mockito spy   method      Actual Code    RunWith PowerMockRunner class   PrepareForTest   Object class  ByteString class     Mock private ByteString mockByteString   String testData      dsfgdshf     PowerMockito when mockByteString toStringUtf8    thenReturn testData       throws above given exception   Solution to fix this issue   1st Remove annotation     Mock      private ByteString mockByteString    2nd Add PowerMockito mock  mockByteString   PowerMockito mock ByteString class

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Missing  MockBean on the bean you want to mock

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This is my case     given ObjectA a   new ObjectA    ObjectB b   mock ObjectB class   when b call    thenReturn a    Target target   spy new Target     doReturn b  when target  method1       when String result   target method2      Then I get this error   org mockito exceptions misusing WrongTypeOfReturnValue   ObjectB  EnhancerByMockitoWithCGLIB  2eaf7d1d cannot be returned by method2   method2   should return String   Can you guess   The problem is that Target method1   is a static method  Mockito completely warns me to another thing

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TL DR If some arguments in your test are null  be sure to mock the parameter call with isNull   instead of anyXXX     I got this error when upgrading from Spring boot 1 5 x to 2 1 x  Spring boot ships with its own Mockito  which is now also upgraded to 2 x  see e g  Dependencies of Spring boot 2 1 2  Mockito has changed the behavior for the anyXXX   method  where XXX is String  Long  etc  Here is the javadoc of anyLong     Since Mockito 2 1 0  only allow valued Long  thus null is not anymore a valid value As primitive wrappers are nullable  the suggested API to match null wrapper would be  isNull    We felt this change would make tests harness much safer that it was with Mockito 1 x   I d suggest you debug to the point where your mock is about to be called and inspect  whether at least one argument is null  In that case make sure  that you prepare your mock with isNull   instead of e g  anyLong    So this  when MockedClass method anyString      becomes  when MockedClass method isNull

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I recently encountered this issue while mocking a function in a Kotlin data class  For some unknown reason one of my test runs ended up in a frozen state  When I ran the tests again some of my tests that had previously passed started to fail with the WrongTypeOfReturnValue exception   I ensured I was using org mockito mockito-inline to avoid the issues with final classes  mentioned by Arvidaa   but the problem remained  What solved it for me was to kill the process and restart Android Studio  This terminated my frozen test run and the following test runs passed without issues

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I recently had this issue  The problem was that the method I was trying to mock had no access modifier  Adding public solved the problem

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According to https   groups google com forum  fromgroups  topic mockito 9WUvkhZUy90  you should rephrase your   when bar getFoo    thenReturn fooBar    to  doReturn fooBar  when bar  getFoo

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For me this meant I was running this   a   Mockito mock SomeClass class   b   new RealClass    when b method1 a   thenReturn c       within this method1  it calls param1 method2   -- note  b is not a spy or mock   So what was happening is that mockito was detecting that a method2   was being called  and telling me I couldn t return c from a method2   which is wrong     Fix  use the doReturn c  when b  method1 a  style syntax  instead of when b method1 a   thenReturn c     which will help you discover the hidden bug more concisely and quickly     Or in this particular case  after doing that it started showing the more accurate  NotAMockException   and I changed it to not longer try to set a return value from a non-mock object

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I m using Scala and I ve got this message where I ve mistakenly shared a Mock between two Objects  So  be sure that your tests are independent of each other  The parallel test execution obviously creates some flaky situations since the objects in Scala are singleton compositions

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In my case the problem was caused by trying to mock a static method and forgetting to call mockStatic on the class  Also I forgot to include the class into the  PrepareForTest

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Very interested problem  In my case this problem was caused when I tried to debug my tests on this similar line   Boolean fooBar  when bar getFoo    thenReturn fooBar     The important note is that the tests were running correctly without debugging   In any way  when I replaced above code with below code snippet then I was able to debug the problem line without problems   doReturn fooBar  when bar  getFoo

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I had this error because in my test I had two expectations  one on a mock and one on concrete type  MyClass cls   new MyClass    MyClass cls2   Mockito mock Myclass class   when foo bar cls   thenReturn       cls is not actually a mock when foo baz cls2   thenReturn      I fixed it by changing cls to be a mock as well

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In my case  I was using both  RunWith MockitoJUnitRunner class  and MockitoAnnotations initMocks this   When I removed MockitoAnnotations initMocks this  it worked correctly

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Another reason for similar error message is trying to mock a final method  One shouldn t attempt to mock final methods  see Final method mocking    I have also confronted the error in a multi-threaded test  Answer by gna worked in that case

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If you are using annotations  may be you need to use  Mock instead of  InjectMocks  Because  InjectMocks works as  Spy and  Mock together  And  Spy keeps track of recently executed methods and you may feel that incorrect data is returned subbed

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In my case the bean has been initialized using  Autowired annotation instead of  MockBean  So in this way mocking of DAOs and Services throws such exception

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I got this issue WrongTypeOfReturnValue because I mocked a method returning a java util Optional  with a com google common base Optional  due to my formatter automatically adding missing imports   Mockito was just saying me that  method something   should return Optional

[java] when I run mockito test occurs WrongTypeOfReturnValue Exception

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