How to mock constructor of nested class with jmockit

Question

I'm trying to use JMockit for unit testing Android apps. It is a little bit tricky since executing the test in the local JVM means that all Android classes are stubs, but you can mock them and that's not a problem.

But now I want to test a method in a nested class that is a subclass of a ResultReceiver. This class is nested in a Fragment. The problem is that when I create this nested class, I want to mock its constructor since it will raise an exception (its is a stub). I have tried to isolate the code and the problem is not with Android but with the class structure. Example:

Base class:

public class JM_base {
  int m_i;

  public JM_base(int i) {
    m_i = i;
  }
}

Nested class:

public class JM_nested_class_cons {
  public class Nested extends JM_base {
    public Nested(int i) {
      super(i);
    }
    public void methodToTest() {
      System.out.print("System under test!");
    }
  }
}

The test:

public class Test_JM_nested_class_cons {
  @Mocked JM_nested_class_cons mock;

  @Test
  public void test() {
    new MockUp<JM_nested_class_cons.Nested>() {
      @Mock public void $init(int i) {
        System.out.println("Hi!");
      }
    };

    JM_nested_class_cons.Nested t = mock.new Nested(1);
    t.methodToTest();
  }
}

As far as I understand, the "real" constructor of Nested() should never be called, and "Hi!" should appear in the console, right ? What am I doing wrong ?

Thx

Answer 1

The problem here is that MockUp treats JM_nested_class_cons.Nested as a regular, non-inner, class. So, it's not taking into account that each constructor has a hidden first parameter for the outer object (JM_nested_class_cons).

A work-around is to explicitly declare this extra parameter in the @Mock method for the constructor of the inner class:

@Mock
void $init(JM_nested_class_cons outer, int i) {
    System.out.println("Hi!");
}