Testing Private method using mockito

Question

public class A        public void method boolean b             if  b    true                 method1              else                method2               private void method1          private void method2           public class TestA         Test     public void testMethod           A a   mock A class         a method true           how to test like    verify a  method1              How to test private method is called or not  and how to test private method using mockito

User · Answer

I don t really understand your need to test the private method  The root problem is that your public method has void as return type  and hence you are not able to test your public method  Hence you are forced to test your private method  Is my guess correct    A few possible solutions  AFAIK     Mocking your private methods  but still you won t be  actually  testing your methods   Verify the state of object used in the method  MOSTLY methods either do some processing of the input values and return an output  or change the state of the objects  Testing the objects for the desired state can also be employed     public class A   SomeClass classObj   null   public void publicMethod       privateMethod       private void privateMethod         classObj   new SomeClass                Here you can test for the private method  by checking the state change of the classObj from null to not null    Refactor your code a little  Hope this is not a legacy code   My funda of writing a method is that  one should always return something  a int  a boolean   The returned value MAY or MAY NOT be used by the implementation  but it will SURELY BE used by the test   code   public class A        public int method boolean b                  int nReturn   0            if  b    true                 nReturn   method1              else                nReturn   method2               private int method1           private int method2

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You can t do that with Mockito but you can use Powermock to extend Mockito and mock private methods  Powermock supports Mockito  Here s an example

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Not possible through mockito  From their wiki     Why Mockito doesn t mock private methods       Firstly  we are not dogmatic about mocking private methods  We just   don t care about private methods because from the standpoint of   testing private methods don t exist  Here are a couple of reasons   Mockito doesn t mock private methods       It requires hacking of classloaders that is never bullet proof and it   changes the api  you must use custom test runner  annotate the class    etc          It is very easy to work around - just change the visibility of method   from private to package-protected  or protected         It requires me to spend time implementing  amp  maintaining it  And it   does not make sense given point  2 and a fact that it is already   implemented in different tool  powermock         Finally    Mocking private methods is a hint that there is something   wrong with OO understanding  In OO you want objects  or roles  to   collaborate  not methods  Forget about pascal  amp  procedural code  Think   in objects

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There is actually a way to test methods from a private member with Mockito  Let s say you have a class like this   public class A       private SomeOtherClass someOtherClass      A             someOtherClass   new SomeOtherClass              public void method boolean b           if  b    true              someOtherClass method1            else             someOtherClass method2              public class SomeOtherClass       public void method1          public void method2          If you want to test a method will invoke a method from SomeOtherClass  you can write something like below    Test public void testPrivateMemberMethodCalled         A a   new A        SomeOtherClass someOtherClass   Mockito spy new SomeOtherClass         ReflectionTestUtils setField  a   someOtherClass   someOtherClass       a method  true         Mockito verify  someOtherClass  Mockito times  1     method1        ReflectionTestUtils setField    will stub the private member with something you can spy on

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You re not suppose to test private methods   Only non-private methods needs to be tested as these should call the private methods anyway   If you  want  to test private methods  it may indicate that you need to rethink your design   Am I using proper dependency injection  Do I possibly needs to move the private methods into a separate class and rather test that  Must these methods be private      can t they be default or protected rather   In the above instance  the two methods that are called  randomly  may actually need to be placed in a class of their own  tested and then injected into the class above

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In cases where the private method is not void and the return value is used as a parameter to an external dependency s method  you can mock the dependency and use an ArgumentCaptor to capture the return value  For example  ArgumentCaptor lt ByteArrayOutputStream gt  csvOutputCaptor   ArgumentCaptor forClass ByteArrayOutputStream class     Do your thing   verify this awsService  uploadFile csvOutputCaptor capture          assertEquals csvOutputCaptor getValue   toString     quot blabla quot

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Put your test in the same package  but a different source folder  src main java vs  src test java  and make those methods package-private  Imo testability is more important than privacy

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Think about this in terms of behaviour  not in terms of what methods there are   The method called method has a particular behaviour if b is true   It has different behaviour if b is false   This means you should write two different tests for method  one for each case   So instead of having three method-oriented tests  one for method  one for method1  one for method2  you have two behaviour-oriented tests   Related to this  I suggested this in another SO thread recently  and got called a four-letter word as a result  so feel free to take this with a grain of salt   I find it helpful to choose test names that reflect the behaviour that I m testing  rather than the name of the method   So don t call your tests testMethod    testMethod1    testMethod2   and so forth   I like names like calculatedPriceIsBasePricePlusTax   or taxIsExcludedWhenExcludeIsTrue   that indicate what behaviour I m testing  then within each test method  test only the indicated behaviour   Most such behaviours will involve just one call to a public method  but may involve many calls to private methods   Hope this helps

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By using reflection  private methods can be called from test classes  In this case     test method will be like this      public class TestA       Test     public void testMethod          A a  new A        Method privateMethod   A class getDeclaredMethod  method1   null       privateMethod setAccessible true          invoke the private method for test     privateMethod invoke A  null             If the private method calls any other private method  then we need to spy the object and stub the another method The test class will be like        test method will be like this      public class TestA       Test     public void testMethod          A a  new A        A spyA   spy a       Method privateMethod   A class getDeclaredMethod  method1   null       privateMethod setAccessible true       doReturn  Test   when spyA   method2       if private method2 is returning string data        invoke the private method for test     privateMethod invoke spyA   null                 The approach is to combine reflection and spying the object    method1 and   method2 are private methods and method1 calls method2

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While Mockito doesn t provide that capability  you can achieve the same result using Mockito   the JUnit ReflectionUtils class or the Spring ReflectionTestUtils class  Please see an example below taken from here explaining how to invoke a private method   ReflectionTestUtils invokeMethod student   saveOrUpdate    From Unit test      Complete examples with ReflectionTestUtils and Mockito can be found in the book Mockito for Spring

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Here is a small example how to do it with powermock  public class Hello       private Hello obj      private Integer method1 Long id            return id   10             To test method1 use code   Hello testObj   new Hello    Integer result   Whitebox invokeMethod testObj   method1   new Long 10L      To set private object obj use this   Hello testObj   new Hello    Hello newObject   new Hello    Whitebox setInternalState testObj   obj   newObject

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I was able to test a private method inside using mockito using reflection  Here is the example  tried to name it such that it makes sense    Service containing the mock method is injected with mockObjects   InjectMocks private ServiceContainingPrivateMethod serviceContainingPrivateMethod     Using reflection to change accessibility of the private method  Class lt   gt    params   new Class lt   gt    PrivateMethodParameterOne class  PrivateMethodParameterTwo class       Method m   serviceContainingPrivateMethod  getClass   getDeclaredMethod  privateMethod   params         making private method accessible     m setAccessible true        assertNotNull m invoke serviceContainingPrivateMethod  privateMethodParameterOne  privateMethodParameterTwo  equals null

[java] Testing Private method using mockito

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