added missing user defined matrix tests

src/UnitTests/LinearAlgebraTests/Double/UserDefinedMatrixTests.cs

@@ -0,0 +1,50 @@
+using System.Collections.Generic;
+using MbUnit.Framework;
+
+namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double
+{
+    using LinearAlgebra.Double;
+
+    internal class UserDefinedMatrix : Matrix
+    {
+        private readonly double[,] _data;
+
+        public UserDefinedMatrix(int rows, int columns) : base(rows, columns)
+        {
+            _data = new double[rows, columns];
+        }
+
+        public UserDefinedMatrix(double[,] data) : base(data.GetLength(0), data.GetLength(1))
+        {
+            _data = data;
+        }
+
+        public override double At(int row, int column)
+        {
+            return _data[row, column];
+        }
+
+        public override void At(int row, int column, double value)
+        {
+            _data[row, column] = value;
+        }
+
+        public override Matrix CreateMatrix(int numberOfRows, int numberOfColumns)
+        {
+            return new UserDefinedMatrix(numberOfRows, numberOfColumns);
+        }
+    }
+
+    public class UserDefinedMatrixTests : MatrixTests
+    {
+        protected override Matrix CreateMatrix(int rows, int columns)
+        {
+            return new UserDefinedMatrix(rows, columns);
+        }
+
+        protected override Matrix CreateMatrix(double[,] data)
+        {
+            return new UserDefinedMatrix(data);
+        }
+    }
+}