new_contents: class assert_raises(object):
  
      def __init__(self, exc_ty):
          self.exc_ty = exc_ty
  
      def __enter__(self):
          pass
  
      def __exit__(self, type, value, traceback):
          if type is None:
              raise AssertionError('Exception not raised')
          if issubclass(type, self.exc_ty):
              return True
          raise AssertionError('Wrong exception raised'), value
  
subject: Test utils