public void NodeDecreaseLevel()
{
var rootNode = new ArneTreeNode <Int32, Int32>(100, 0);
var aNode = new ArneTreeNode <Int32, Int32>(90, 4);
var bNode = new ArneTreeNode <Int32, Int32>(20, 1);
var cNode = new ArneTreeNode <Int32, Int32>(120, 3);
var dNode = new ArneTreeNode <Int32, Int32>(10, 5);
var eNode = new ArneTreeNode <Int32, Int32>(30, 3);
// initialize
rootNode.Left = aNode;
aNode.Left = bNode;
aNode.Right = cNode;
bNode.Left = dNode;
bNode.Right = eNode;
// perform opeation
Assert.AreEqual(dNode, dNode.DecraseLevel());
Assert.AreEqual(eNode, eNode.DecraseLevel());
aNode.DecraseLevel();
Assert.AreEqual(2u, aNode.Level);
Assert.AreEqual(2u, aNode.Right.Level);
}