gistfile1.cs

public static class ThingTestingUtilities {
  public static Thing NewThing(this TestsThings tester) {
    return new MyThing;
  }

  public static Thing WithDueDate(this MyThing thing, DateTime duedate) {
    thing.DueDate = duedate;
    return thing;
  }

  public static Thing WithAnOffsetDueDateInDays(this MyThing thing, int days){
    return thing.WithDueDate(DateTime.Now.AddDays(days));
  }
}