message: Add test case for builtin len() support of tf.data.Dataset in autograph
diff: @@ -123,6 +123,13 @@ class PyBuiltinsTest(test.TestCase):
  tl = py_builtins.len_(data_structures.tf_tensor_list_new([3, 4, 5]))
  self.assertEqual(self.evaluate(tl), 3)
  + def test_len_dataset(self):
  + dataset = dataset_ops.DatasetV2.from_tensor_slices([3, 2, 1])
  + self.assertEqual(py_builtins.len_(dataset), 3)
  + with self.cached_session() as sess:
  + t = py_builtins.len_(dataset)
  + self.assertAllEqual(self.evaluate(t), 3)
  +
  def test_len_scalar(self):
  with self.assertRaises(ValueError):
  py_builtins.len_(constant_op.constant(1))
  