GenericallyUgly.cs

public abstract class Thing
{
}

public interface IMarker {}

public interface IUseful<T> : IMarker where T : Thing
{
  T DoSomething();
}

public class Useful<T> : IUseful<T> where T : Thing
{
  T DoSomething()
  {
    // ...
  }
}

public class When_extracting_non_marker_interfaces
{
  static Type[] _interfaces;

  Establish context =()=>
    _interfaces = typeof(Useful<>).GetInterfaces()
        .Where(i=>i.IsGenericType)
        .Select(i=>i.GetGenericTypeDefinition());

  Because of =()=>
    // What goes here to make the following assertion pass?

  It the_useful_interface_is_extracted =()=>
    _interfaces.ShouldContain( typeof(IUseful<>) );
}