How to mock private method for testing using PowerMock

Question

I have a class which I would like to test with a public method that calls private one  I d like to assume that private method works correctly  For example  I d like something like doReturn    when     I found that there is possible solution using PowerMock  but this solution doesn t work for me  How It can be done  Did anybody have this problem

User · Answer

A generic solution that will work with any testing framework (if your class is non-final) is to manually create your own mock.

Change your private method to protected.
In your test class extend the class
override the previously-private method to return whatever constant you want

This doesn't use any framework so its not as elegant but it will always work: even without PowerMock. Alternatively, you can use Mockito to do steps #2 & #3 for you, if you've done step #1 already.

To mock a private method directly, you'll need to use PowerMock as shown in the other answer.

User · Answer

i know a way ny which you can call you private function to test in mockito    Test     public  void  commandEndHandlerTest   throws  Exception               Method retryClientDetail privateMethod  yourclass class getDeclaredMethod  Your function name  null           retryClientDetail privateMethod setAccessible true           retryClientDetail privateMethod invoke yourclass class  null

User · Answer

I don t see a problem here  With the following code using the Mockito API  I managed to do just that    public class CodeWithPrivateMethod        public void meaningfulPublicApi             if  doTheGamble  Whatever   1  lt  lt  3                 throw new RuntimeException  boom                         private boolean doTheGamble String whatever  int binary            Random random   new Random System nanoTime             boolean gamble   random nextBoolean            return gamble            And here s the JUnit test    import org junit Test  import org junit runner RunWith  import org powermock api mockito PowerMockito  import org powermock core classloader annotations PrepareForTest  import org powermock modules junit4 PowerMockRunner  import static org mockito Matchers anyInt  import static org mockito Matchers anyString  import static org powermock api mockito PowerMockito when  import static org powermock api support membermodification MemberMatcher method    RunWith PowerMockRunner class   PrepareForTest CodeWithPrivateMethod class  public class CodeWithPrivateMethodTest         Test expected   RuntimeException class      public void when gambling is true then always explode   throws Exception           CodeWithPrivateMethod spy   PowerMockito spy new CodeWithPrivateMethod              when spy  method CodeWithPrivateMethod class   doTheGamble   String class  int class                    withArguments anyString    anyInt                     thenReturn true            spy meaningfulPublicApi

User · Answer

With no argument   ourObject   PowerMockito spy new OurClass     when ourObject    ourPrivateMethodName   thenReturn  mocked result      With String argument   ourObject   PowerMockito spy new OurClass     when ourObject  method OurClass class   ourPrivateMethodName   String class                    withArguments anyString    thenReturn  mocked result

User · Answer

For some reason Brice s answer is not working for me  I was able to manipulate it a bit to get it to work  It might just be because I have a newer version of PowerMock  I m using 1 6 5   import java util Random   public class CodeWithPrivateMethod        public void meaningfulPublicApi             if  doTheGamble  Whatever   1  lt  lt  3                 throw new RuntimeException  boom                         private boolean doTheGamble String whatever  int binary            Random random   new Random System nanoTime             boolean gamble   random nextBoolean            return gamble            The test class looks as follows   import org junit Test  import org junit runner RunWith  import org powermock api mockito PowerMockito  import org powermock core classloader annotations PrepareForTest  import org powermock modules junit4 PowerMockRunner   import static org mockito Matchers anyInt  import static org mockito Matchers anyString  import static org powermock api mockito PowerMockito doReturn    RunWith PowerMockRunner class   PrepareForTest CodeWithPrivateMethod class  public class CodeWithPrivateMethodTest       private CodeWithPrivateMethod classToTest        Test expected   RuntimeException class      public void when gambling is true then always explode   throws Exception           classToTest   PowerMockito spy classToTest            doReturn true  when classToTest   doTheGamble   anyString    anyInt              classToTest meaningfulPublicApi

[java] How to mock private method for testing using PowerMock?

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