public void SummingMatrices_CorrectParams_ExpectedResult()
        {
            int[,] arr1 = { { 1, 2 }, { 2, 4 } };
            SymmetricMatrix <int> m1 = new SymmetricMatrix <int>(arr1);

            int[,] arr2 = { { 1, 2, 3 }, { 1, 2, 3 }, { 1, 2, 3 } };
            SquareMatrix <int> m2 = new SquareMatrix <int>(arr2);

            Matrix <int> matrix   = m1.SumMatrices(m2);
            int          expected = 6;

            int actual = matrix[1, 1];

            Assert.AreEqual(expected, actual);
        }