public void TrimExcess_doesnt_throw()
        {
            var bigData   = CreateTestData();
            var smallData = CreateTestData(10);

            var hashSet = new ObservableHashSet <int>(bigData.Concat(smallData));

            foreach (var item in bigData)
            {
                hashSet.Remove(item);
            }

            hashSet.TrimExcess();
        }