public void AddSumNode()
{
var xmlDoc = new XmlDocument(TestUtility.CreateDefaultNSM().NameTable);
xmlDoc.LoadXml(
$@"<rowItems xmlns=""http://schemas.openxmlformats.org/spreadsheetml/2006/main"" count=""3"">
<i>
<x v=""1""/>
</i>
<i r=""1"">
<x v=""2""/>
</i>
<i r=""1"">
<x v=""3""/>
</i>
</rowItems>" );
var node = xmlDoc.FirstChild;
var itemsCollection = new ItemsCollection(TestUtility.CreateDefaultNSM(), node);
itemsCollection.AddSumNode("grand");
Assert.AreEqual(4, itemsCollection.Count);
Assert.AreEqual(4, node.ChildNodes.Count);
Assert.AreEqual("grand", itemsCollection[3].ItemType);
}