WIP adding unit tests for batch processing

src/Microsoft.SqlTools.ServiceLayer/QueryExecution/ResultSet.cs

@@ -3,8 +3,11 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 //
 
+using System;
 using System.Collections.Generic;
 using System.Data.Common;
+using System.Linq;
+using Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts;
 
 namespace Microsoft.SqlTools.ServiceLayer.QueryExecution
 {
@@ -33,5 +36,33 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution
             }
             Rows.Add(row.ToArray());
         }
+
+        /// <summary>
+        /// Generates a subset of the rows from the result set
+        /// </summary>
+        /// <param name="startRow">The starting row of the results</param>
+        /// <param name="rowCount">How many rows to retrieve</param>
+        /// <returns>A subset of results</returns>
+        public ResultSetSubset GetSubset(int startRow, int rowCount)
+        {
+            // Sanity check to make sure that the row and the row count are within bounds
+            if (startRow < 0 || startRow >= Rows.Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(startRow), "Start row cannot be less than 0 " +
+                                                                        "or greater than the number of rows in the resultset");
+            }
+            if (rowCount <= 0)
+            {
+                throw new ArgumentOutOfRangeException(nameof(rowCount), "Row count must be a positive integer");
+            }
+
+            // Retrieve the subset of the results as per the request
+            object[][] rows = Rows.Skip(startRow).Take(rowCount).ToArray();
+            return new ResultSetSubset
+            {
+                Rows = rows,
+                RowCount = rows.Length
+            };
+        }
     }
 }