new_contents: from cleverhans.dataset import Dataset
  
  class LightweightDataset(Dataset):
      """
      A dataset that does not actually load any data so it is cheap to run
      in tests.
      """
  
  
  def test_factory():
      d1 = LightweightDataset()
      factory = d1.get_factory()
      d2 = factory()
      assert type(d1) == type(d2)
  
subject: test that catches the previous two bugs