Adding EditCell constructor validation (#301)

* New unit tests!
* New CopyTo method!
* New null validation!

YEAH!!!

test/Microsoft.SqlTools.ServiceLayer.UnitTests/EditData/EditCellTests.cs

@@ -0,0 +1,47 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System;
+using Microsoft.SqlTools.ServiceLayer.EditData.Contracts;
+using Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts;
+using Xunit;
+
+namespace Microsoft.SqlTools.ServiceLayer.UnitTests.EditData
+{
+    public class EditCellTests
+    {
+        [Fact]
+        public void ConstructNullDbCell()
+        {
+            // If: I construct an EditCell with a null DbCellValue
+            // Then: It should throw
+            Assert.Throws<ArgumentNullException>(() => new EditCell(null, true));
+        }
+
+        [Fact]
+        public void ConstructValid()
+        {
+            // Setup: Create a DbCellValue to copy the values from
+            DbCellValue source = new DbCellValue
+            {
+                DisplayValue = "qqq",
+                IsNull = true,
+                RawObject = 12
+            };
+
+            // If: I construct an EditCell with a valid DbCellValue
+            EditCell ec = new EditCell(source, true);
+
+            // Then:
+            // ... The values I provided in the DbCellValue should be present
+            Assert.Equal(source.DisplayValue, ec.DisplayValue);
+            Assert.Equal(source.IsNull, ec.IsNull);
+            Assert.Equal(source.RawObject, ec.RawObject);
+
+            // ... The is dirty value I set should be present
+            Assert.True(ec.IsDirty);
+        }
+    }
+}