How to mock local object creations in JUnit

Question

I am not aware about how to mock local objects within a method using JUnit and mockito.

JDK - 1.7, JUnit - 4.12, powermock-module-junit4 - 1.6.6, powermock-api-mockito - 1.6.6

Also, bringing in the point that I must use only JDK 1.7.

In the below sample class, how do mock "service" object which is at method scope.

class A {
public String methodA() {

SampleService service = new SampleService();
return service.retrieveValue();

}
}

Please suggest.

Answer 1

You can't mock local variable. But you can do following:

1) Create a Factory and inject int o tested class. After that refactoring you could mock the factory and provide mocked service to tested object.

class A {
    private SampleServiceFactory factory;
    public String methodA() {
        SampleService service = factory.createSampleService();
        return service.retrieveValue();
    }
}

In test you should inject factory mock and after that return mock of the service on createSampleService() call:

when(mockFactory.retrieveValue()).thenReturn(mockService);

2) You can extract method and override it in the test and return mock instead of the implementation:

class A {
    public String methodA() {
        SampleService service = createSampleService();
        return service.retrieveValue();
    }

   protected SampleService createSampleService() {
     return new SampleService();
   }
}

In this approach you can do following: @Test

public void testServiceCall() {
   A testedObject = new A() {
       @Override
       protected SampleService createSampleService() {
         return mockSampleService;
       }
   }
   ...
   testedObject.methodA();
   ...
   verify(service).retrieveValue();
}

PS: I would prefer first one, access modifier changing is not the best approach by my opinion.