在监视子类之前在Mockito中模拟超级类方法

Question

I have a class which I need to test.

public class Mockz extends AnotherClass{
    final MyOtherClass = getMyOtherClass(); // method in AnotherClass
    Integer num = 10;
    protected void method1(){
        System.out.println("in method 1");
    }

    protected void method2(){
        System.out.println("in method 1");
    }
}

And in my test class I have a method like ,

@Test
public testMethod1(){
    final Mockz mockz = Mockito.spy(new Mockz()); // line 1
    Mockito.when(mockz.method1()).thenReturn("Mocking method 1");
    System.out.println(mockz.method1());
}

I think I need to mock the getMyOtherClass() method in the super class, Since when executing line 1 that method gets called.

how can I do that ? Or what is the best way to do this ?

Answer 1

This is purely a problem of class structure: You shouldn't need to (or want to) mock a superclass. When testing, you should test the entirety of your subclass (Mockz), even the parts that apply to the superclass (AnotherClass); otherwise, how would you know that the subclass is fulfilling the entirety of the superclass's contract?

If you're looking to refactor, you may consider switching to a composition/delegate pattern:

public class Mockz implements AnotherInterface {
  private final AnotherClass delegate;

  public Mockz() { this(new AnotherClass()); }

  /** for testing */
  Mockz(AnotherClass delegate) { this.delegate = delegate; }

  // ...
}

...or consider testing a subclass of your subclass:

@Test
public testMethod1(){
    final Mockz mockz = Mockito.spy(new Mockz() {
      @Override public OtherClass getMyOtherClass() {}
    });
    Mockito.when(mockz.method1()).thenReturn("Mocking method 1");
    System.out.println(mockz.method1());
}

...but that second one implies that getMyOtherClass is dangerous enough to warrant mocking, which probably means it shouldn't be a part of your object's constructor code path anyway, leading to the third answer: Don't call a "heavy-lifting" method on your initialization path:

public class Mockz extends AnotherClass{
    MyOtherClass myOtherClass;

    /** Part of construction, but expensive enough to call explicitly. */
    void initializeMyOtherClass() {
        myOtherClass = getMyOtherClass();
    }
}