How to properly unit test a property change?

Question

I have this test:

@Test
public void UpdateAllFooDatesToOneDayBeforeProvidedDate_TodaysDateAndFooDate_UpdatedDates() {
    // arrange
    List<Foo> foos = new ArrayList<Foo>();
    Date barDate = today;
    Foo foo1 = setupFoo();
    Foo foo2 = setupFoo();
    foos.add(foo1);
    foos.add(foo2);
    foo1.setValidTo(dateUtil.adjustDaysOfDate(today, 5));
    foo2.setValidTo(dateUtil.adjustDaysOfDate(today, 8));

    // act
    modifyDates.updateAllFooDatesToOneDayBeforeProvidedDate(barDate, foos);

    // assert
    assertThat(foos, hasItems(...?)); //I don't know how to assert this
}

updateAllFooDatesToOneDayBeforeProvidedDate(Date, List) simply changes a date property of all Foos to the day before barDate.

I am trying to use Hamcrest to help me assert that the list has been updated, but I can't really get it to work.

Should I simply use foos.get(n).getDate() and assert on those?

What is the preferred way of asserting that the date property of the elements in foos has been updated properly?

Edit: Typo

Answer 1

Aren't you making it hard on yourself here? Why not just iterate over the collection and assert for each element?

for ( Foo foo : foos ) { assertThat( foo.getDate() , equalTo( barDate ) ); }

Cheers,