Unit testing with mockito for constructors

Question

I have one class   Class First        private Second second       public First int num  String str            second   new Second str           this num   num                    some other methods     I want to write unit tests for public methods of class First  I want to avoid execution of constructor of class Second   I did this   Second second   Mockito mock Second class   Mockito when new Second any String class    thenReturn null   First first   new First null  null     It is still calling constructor of class Second  How can i avoid it

User · Answer

Mockito can now mock constructors  since version 3 5 0  https   javadoc io static org mockito mockito-core 3 5 13 org mockito Mockito html mocked construction try  MockedConstruction mocked   mockConstruction Foo class        Foo foo   new Foo       when foo method    thenReturn  quot bar quot       assertEquals  quot bar quot   foo method        verify foo  method

User · Answer

I believe  it is not possible to mock constructors using mockito  Instead  I suggest following approach  Class First       private Second second      public First int num  String str         if second   null                  when junit runs  you get the mocked object not null   hence don t           initialize                    second   new Second str               this num   num                  some other methods     And  for test   class TestFirst       InjectMock     First first   inject mock the real testable class      Mock     Second second      testMethod               now you can play around with any method of the Second class using its            mocked object second  like          when second getSomething String class   thenReturn null

User · Answer

You can use PowerMockito  See the example   Second second   Mockito mock Second class   whenNew Second class  withNoArguments   thenReturn second     But re-factoring is better decision

User · Answer

Include this line on top of your test class   PrepareForTest   First class

User · Answer

Once again the problem with unit-testing comes from manually creating objects using new operator  Consider passing already created Second instead   class First      private Second second     public First int num  Second second        this second   second      this num   num            some other methods        I know this might mean major rewrite of your API  but there is no other way  Also this class doesn t have any sense   Mockito when new Second any String class  thenReturn null       First of all Mockito can only mock methods  not constructors  Secondly  even if you could mock constructor  you are mocking constructor of just created object and never really doing anything with that object

User · Answer

Here is the code to mock this functionality using PowerMockito API   Second mockedSecond   PowerMockito mock Second class   PowerMockito whenNew Second class  withNoArguments   thenReturn mockedSecond     You need to use Powermockito runner and need to add required test classes  comma separated   which are required to be mocked by powermock API     RunWith PowerMockRunner class   PrepareForTest  First class Second class   class TestClassName         your testing code

User · Answer

I have used  Pattern 2 - the  factory helper pattern      Pattern 2 - the factory helper pattern      One case where this pattern won t work is if MyClass is final  Most of the Mockito framework doesn t play particularly well with final classes  and this includes the use of spy    Another case is where MyClass uses getClass   somewhere  and requires the resulting value to be MyClass  This won t work  because the class of a spy is actually a Mockito-generated subclass of the original class       In either of these cases  you ll need the slightly more robust factory helper pattern  as follows    public class MyClass    static class FactoryHelper        Foo makeFoo  A a  B b  C c              return new Foo  a  b  c                            private FactoryHelper helper    public MyClass  X x  Y y          this  x  y  new FactoryHelper             MyClass  X x  Y  y  FactoryHelper helper                        this helper   helper                   Foo foo   helper makeFoo  a  b  c            So  you have a special constructor  just for testing  that has an additional argument  This is used from your test class  when creating the object that you re going to test  In your test class  you mock the FactoryHelper class  as well as the object that you want to create     Mock private MyClass FactoryHelper mockFactoryHelper   Mock private Foo mockFoo  private MyClass toTest        and you can use it like this   toTest   new MyClass  x  y  mockFactoryHelper     when  mockFactoryHelper makeFoo     any  A class    any  B class    any  C class        thenReturn  mockFoo        Source  http   web archive org web 20160322155004 http   code google com p mockito wiki MockingObjectCreation

[java] Unit testing with mockito for constructors

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