Mockito.spy not changing real object

Question

Calling method on spy object somehow has no effect on real spied object:

public class AAA {
    public int a;

    public void setA(int aa) {
        this.a = aa;
    }

    public int getA() {
        return a;
    }
}


public class Proof {
    @Test
    public void wtf() {
        AAA obj = new AAA();
        AAA spy = Mockito.spy(obj);

        spy.setA(22);

        assertThat(obj.getA(), equalTo(22));
    }
}

How can that be? I suppose Proof test should pass.

Answer 1

As seen in the Mockito doc:

Mockito does not delegate calls to the passed real instance, instead it actually creates a copy of it.

This means that the original object obj isn't modify with what happens in the spied object spy.

Answer 2

I did some tests and you should make the assert on spy not an obj:

@Test
    public void wtf() {
        AAA obj = new AAA();
        AAA spy = Mockito.spy(obj);

        spy.setA(22);

        assertThat(spy.getA(), equalTo(22));
    }