public void DiagonalSquareMatrix_Add_DiagonalSquareMatrix()
        {
            int[,] inputMatrixFirst = { {            4, default(int), default(int) },
                                        { default(int),            2, default(int) },{ default(int), default(int), 2 } };

            BaseMatrix <int> firstMatrix = new DiagonalSquareMatrix <int>(inputMatrixFirst);

            BaseMatrix <int> secondMatrix = new DiagonalSquareMatrix <int>(inputMatrixFirst);

            var resultSumm = firstMatrix.Add(secondMatrix);

            int[,] resultMatrix = { { 8, 0, 0 }, { 0, 4, 0 }, { 0, 0, 4 } };

            var resultHelper = new DiagonalSquareMatrix <int>(resultMatrix);

            var helper = new HelperForSumm <int>();

            Assert.IsTrue(helper.IsEqual(resultHelper, resultSumm));
        }