public void AddTailTest()
{
// Arrange
var list = new SimpleLinkedList <int>();
list.AddTail(1);
list.AddTail(2);
list.AddTail(3);
list.AddTail(4);
// Act => Assert
list.Head.Should().Be(1);
list.Tail.Should().Be(4);
list.Count.Should().Be(4);
}