class BaseService {
    public void save() {
      // a lot of code here! I cannot change this code.
    }
}

public Childservice extends BaseService {
    public void save(){
        //logic for testing
        super.save();
       //logic for testing
    }
}

public class Parent {
    public int save() {
         return 99;
    }
}

public class Child extends Parent {
    public int save() {
        int i = super.save();
        return i*2;
    }
}

@RunWith(PowerMockRunner.class)
@PrepareForTest(Parent.class)
public class ParentTest {
    @Test
    public void testSave() {
        PowerMockito.suppress(PowerMockito.methodsDeclaredIn(Parent.class));
        System.out.println(new Child().save());
    }
}

public class Bar {
    public void bar() {
        System.out.println("Bar#bar()");
    }
    public int numBar() {
        System.out.println("Bar#numBar()");
        return 99;
    }
}

public class Foo extends Bar {

    @Override
    public void bar() {
        super.bar();
        System.out.println("Foo#bar()");
    }

    @Override
    public int numBar() {
        System.out.println("Foo#numBar() - before-call super.numBar()");
        int result = super.numBar();
        System.out.println("Foo#numBar() - after-call super.numBar();");
        return result;
    }
}

import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

@RunWith(PowerMockRunner.class)
@PrepareForTest(Bar.class)
public class FooTest {
    @Test
    public void testNumBar() throws Exception {
        Foo foo = new Foo();
        Foo fooSpy = Mockito.spy(foo);

        Mockito.doReturn(10).when((Bar) fooSpy).numBar();
        Assert.assertEquals(10, fooSpy.numBar());
    }
}