better tests


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13635 e27351fd-9f3e-4f54-a53b-843176b1656c
test_groupChangeSpanningEvent -> test_groupChangeSmallerSpanningEvent, test_groupChangeLargerSpanningEvent


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13636 e27351fd-9f3e-4f54-a53b-843176b1656c