public void IsProperSubsetOf_NullOther_ArgumentNullException()
 => Assert.Catch <ArgumentNullException>(() => _filledIntSet.IsProperSubsetOf(null));
        public bool IsProperSubsetOf_IntValues_CorrectResult(int[] set, int[] subset)
        {
            AddValues(set);

            return(_intSet.IsProperSubsetOf(subset));
        }