Mockito spy - when calling inner class method not spying method in spy object

Question

I have class with inner class as following:

public class ClassWithInnerObject {

  private final InnerObject innerObject;

  public ClassWithInnerObject() {
    innerObject = new InnerObject();
  }

  public void callInnerObjectMethod() {
    innerObject.outerFunc();
  }

  public void outerFunc() {
    innerFunc();
  }

  public void innerFunc() {
    Log.d("XXX", "innerFunc: called");
  }

  public class InnerObject {
    public void outerFunc() {
      innerFunc();
    }
  }
}

And the mockito test is looking as following: build.gradle:

  androidTestCompile 'junit:junit:4.12'
  androidTestCompile 'org.mockito:mockito-core:1.10.19'

  androidTestCompile 'com.crittercism.dexmaker:dexmaker:1.4'
  androidTestCompile 'com.crittercism.dexmaker:dexmaker-mockito:1.4'
  androidTestCompile 'com.crittercism.dexmaker:dexmaker-dx:1.4'

Test:

@RunWith(AndroidJUnit4.class) public class SpyVerifyTest {

  @Test public void myInnerTestWorking() {
    ClassWithInnerObject p = new ClassWithInnerObject();
    ClassWithInnerObject spy = Mockito.spy(p);
    spy.outerFunc();
    verify(spy, times(1)).innerFunc();
  }


  @Test public void myInnerTestNotWorking() {
    ClassWithInnerObject p = new ClassWithInnerObject();
    ClassWithInnerObject spy = Mockito.spy(p);
    spy.callInnerObjectMethod();
    verify(spy, times(1)).innerFunc();
  }

}

The first test is working as expected. The second one the innerFunc is never detected as "invoked", although in the log I see it is.What is wrong? :)

Thanks!

Answer 1

What is wrong?

Well, the problem here is quite subtle, when you call Mockito.spy(p), mockito creates behind the scene some kind of decorator over your instance of ClassWithInnerObject allowing to monitor all methods calls on your instance. Thanks to that, you can check how many times a given method has been called but on the decorator only not on your instance. And here, when you use an inner class, it calls innerFunc() on your instance of ClassWithInnerObject not on the decorator so for Mockito innerFunc() has not been called.