Public ReadOnly Property First As TNode

public TNode First {get;}

LListNode<string> empty = new LListNode<string>();
LListNode<string> valueA = new LListNode<string>("A");
LListNode<string> valueB = new LListNode<string>("B");
LListNode<string>.LList list = new LListNode<string>.LList();

list.AddFirst(empty);
Assert.AreEqual(1, list.Count);
Assert.AreEqual(empty, list.First);
Assert.AreEqual(empty, list.Last);
Assert.IsNull(empty.Next);
Assert.IsNull(empty.Previous);

list.AddLast(valueB);
Assert.AreEqual(2, list.Count);
Assert.AreEqual(empty, list.First);
Assert.AreEqual(valueB, list.Last);

Assert.AreEqual(valueB, empty.Next);
Assert.IsNull(empty.Previous);

Assert.AreEqual(empty, valueB.Previous);
Assert.IsNull(valueB.Next);

list.AddFirst(valueA);
Assert.AreEqual(3, list.Count);
Assert.AreEqual(valueA, list.First);
Assert.AreEqual(valueB, list.Last);

Assert.AreEqual(valueB, empty.Next);
Assert.AreEqual(valueA, empty.Previous);

Assert.AreEqual(empty, valueA.Next);
Assert.IsNull(valueA.Previous);

Assert.AreEqual(empty, valueB.Previous);
Assert.IsNull(valueB.Next);

list.Remove(empty);
Assert.AreEqual(2, list.Count);
Assert.AreEqual(valueA, list.First);
Assert.AreEqual(valueB, list.Last);

Assert.AreEqual(valueB, valueA.Next);
Assert.IsNull(valueA.Previous);

Assert.AreEqual(valueA, valueB.Previous);
Assert.IsNull(valueB.Next);

Dim empty As New LListNode(Of String)()
Dim valueA As New LListNode(Of String)("A")
Dim valueB As New LListNode(Of String)("B")
Dim list As New LListNode(Of String).LList()

list.AddFirst(empty)
Assert.AreEqual(1, list.Count)
Assert.AreEqual(empty, list.First)
Assert.AreEqual(empty, list.Last)
Assert.IsNull(empty.[Next])
Assert.IsNull(empty.Previous)

list.AddLast(valueB)
Assert.AreEqual(2, list.Count)
Assert.AreEqual(empty, list.First)
Assert.AreEqual(valueB, list.Last)

Assert.AreEqual(valueB, empty.[Next])
Assert.IsNull(empty.Previous)

Assert.AreEqual(empty, valueB.Previous)
Assert.IsNull(valueB.[Next])

list.AddFirst(valueA)
Assert.AreEqual(3, list.Count)
Assert.AreEqual(valueA, list.First)
Assert.AreEqual(valueB, list.Last)

Assert.AreEqual(valueB, empty.[Next])
Assert.AreEqual(valueA, empty.Previous)

Assert.AreEqual(empty, valueA.[Next])
Assert.IsNull(valueA.Previous)

Assert.AreEqual(empty, valueB.Previous)
Assert.IsNull(valueB.[Next])

list.Remove(empty)
Assert.AreEqual(2, list.Count)
Assert.AreEqual(valueA, list.First)
Assert.AreEqual(valueB, list.Last)

Assert.AreEqual(valueB, valueA.[Next])
Assert.IsNull(valueA.Previous)

Assert.AreEqual(valueA, valueB.Previous)
Assert.IsNull(valueB.[Next])