class Fruit {}
class Banana : Fruit {}

[Test]
public void CanAssignBananaToFruit()
{
 var fruit = typeof (Fruit);
 var banana = typeof (Banana);
 Assert.IsTrue(fruit.IsAssignableFrom(banana));
}

[Test]
public void CanNotAssignFruitToBanana()
{
 var fruit = typeof(Fruit);
 var banana = typeof(Banana);
 Assert.IsFalse(banana.IsAssignableFrom(fruit));
}

I really hate this API because it always seems backward to me. Here is how i really want to use it:

Assert.IsTrue(banana.CanBeAssignedTo(fruit));
Assert.IsFalse(fruit.CanBeAssignedTo(banana));

With the aid of an extension method we can easily achieve this:

public static bool CanBeAssignedTo(this Type sourceType, Type destinationType)
{
 return destinationType.IsAssignableFrom(sourceType);
}

class Program
{
 [STAThread]
 static void Main()
 {
  var itunes = new iTunesApp();
  itunes.DeleteTracksThatDoNotExist();
 }
}

public static class ITunesExtensions
{
 public static void DeleteTracksThatDoNotExist(this IiTunes itunes)
 {
  var tracksThatDoNotExist = FindTracksThatDoNotExist(itunes);
  foreach (var track in tracksThatDoNotExist) track.Delete();
 }

 public static IEnumerable<IITFileOrCDTrack> FindTracksThatDoNotExist(this IiTunes iTunes)
 {
  return iTunes.LibraryPlaylist.Tracks
   .OfType<IITFileOrCDTrack>()
   .Where(track => !File.Exists(track.Location));
 }
}