public void TestCase()
{
IList<string> list = new System.Collections.Generic.List<string> {
"First", "Second", "Third"
};
var enumerator = list.GetLoopedTwoWayEnumerator ();
Assert.AreEqual (null, enumerator.Current);
Assert.IsTrue (enumerator.MoveNext ());
Assert.AreEqual ("First", enumerator.Current);
Assert.IsTrue (enumerator.MoveNext ());
Assert.AreEqual ("Second", enumerator.Current);
Assert.IsTrue (enumerator.MoveNext ());
Assert.AreEqual ("Third", enumerator.Current);
Assert.IsTrue (enumerator.MoveNext ());
Assert.AreEqual ("First", enumerator.Current);
Assert.IsTrue (enumerator.MoveNext ());
Assert.AreEqual ("Second", enumerator.Current);
// обратный ход
Assert.IsTrue (enumerator.MovePrevious ());
Assert.AreEqual ("First", enumerator.Current);
Assert.IsTrue (enumerator.MovePrevious ());
Assert.AreEqual ("Third", enumerator.Current);
Assert.IsTrue (enumerator.MovePrevious ());
Assert.AreEqual ("Second", enumerator.Current);
Assert.IsTrue (enumerator.MovePrevious ());
Assert.AreEqual ("First", enumerator.Current);
Assert.IsTrue (enumerator.MovePrevious ());
Assert.AreEqual ("Third", enumerator.Current);
Assert.IsTrue (enumerator.MoveNext ());
Assert.AreEqual ("First", enumerator.Current);
}