code: def testElementwiseOpUnknownRankError(self):
      if context.executing_eagerly():
          return
      x = ragged_factory_ops.constant([[1, 2], [3]])
      y = ragged_tensor.RaggedTensor.from_row_splits(
          array_ops.placeholder_with_default([1, 2, 3], shape=None),
          x.row_splits,
      )
      with self.assertRaisesRegex(
          ValueError, r"Unable to broadcast: unknown rank"
      ):
          math_ops.add(x, y)
  
imports: from absl.testing import parameterized
  import numpy
  from tensorflow.python import tf2
  from tensorflow.python.eager import context
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import errors
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import random_seed
  from tensorflow.python.framework import sparse_tensor
  from tensorflow.python.framework import tensor
  from tensorflow.python.framework import test_util
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import array_ops_stack
  from tensorflow.python.ops import check_ops
  from tensorflow.python.ops import clip_ops
  from tensorflow.python.ops import data_flow_ops
  from tensorflow.python.ops import image_ops_impl
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import nn_impl
  from tensorflow.python.ops import nn_ops
  from tensorflow.python.ops import string_ops
  from tensorflow.python.ops import variables
  from tensorflow.python.ops.ragged import ragged_dispatch
  from tensorflow.python.ops.ragged import ragged_factory_ops
  from tensorflow.python.ops.ragged import ragged_tensor
  from tensorflow.python.ops.ragged import ragged_tensor_test_ops
  from tensorflow.python.ops.ragged.dynamic_ragged_shape import DynamicRaggedShape
  from tensorflow.python.platform import googletest
  from tensorflow.python.util import dispatch
  from tensorflow.python.util import nest
label_desc: Use image node_id 7 for calling the RaggedDispatchTest obj's underlying member method code with example usage: obj.testElementwiseOpUnknownRankError() without return types