java - Mockito.spy not changing real object -

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 be? suppose proof test should pass.

as seen in mockito doc:

mockito does not delegate calls passed real instance, instead creates copy of it.

this means original object obj isn't modify happens in spied object spy.