How to change parameter passed to a method using mocking

Question

Imagine classes as below

public class Foo {

     public void storeThis(Object obj, long storeTime){
           //store the obj with storeTime
     }
}

public class Bar {
     public void someOperation(){
           //doSomething
           BarUtils.storeMe(obj);
     }
}

public class BarUtils {
     Foo _f = new Foo();
     static void storeMe(Object obj){
          //doSomething
          _f.storeThis(obj, System.currentmillis());
     }
}

Now I am testing the Foo.storeThis(obj, time), for that, I need to add different time cases. How can I change/mock the parameter of a method? (Considering I need to mock Foo.storeThis()). How can I achieve this? Can I mock a method so that only its parameter is changed and the implementation is the same as the actual method?

Edit: I cannot directly invoke Foo.storeThis(), Since I need to test the functionality of Bar.someOperation() and I cannot randomly put obj into Foo.storeThis().

Answer 1

Solution: I got the solution for what I needed. It turns out that I can use a mocked class and an invocation.proceed() method to achieve the above. Here is a code example (as a continuation of my example in question).

public class FooMock extends MockUp<Foo> {
   private long newStoreTime;

   public void setTimeToBeMocked(long storeTime) {
      newStoreTime = storeTime;
   }
   public void storeThis(Invocation inv, Object obj, long storeTime){
           inv.proceed(obj, newStoreTime);
     }
}

In my test class :

public class BarTest {
      @Test
      public void testSomeOperation(long testInTime){
          FooMock mock = new FooMock();
          Bar bar = new Bar();
          mock.setTimeToBeMocked(testInTime);
          bar.someOperation();//This would store obj in testInTime
      }
}

Thanks