code: def testRaggedToStringUnknownRank(self):
      @def_function.function(
          input_signature=[
              ragged_tensor.RaggedTensorSpec(
                  ragged_rank=1, dtype=dtypes.int32
              )
          ]
      )
      def f(rt):
          return ragged_string_ops.ragged_tensor_to_string(rt)
  
      with self.assertRaisesRegex(
          ValueError,
          "RaggedTensor to_string requires "
          "that rt.shape.rank is not None",
      ):
          f(ragged_factory_ops.constant([[1, 2], [3]]))
  
imports: import os.path
  import tempfile
  from absl.testing import parameterized
  from tensorflow.python.eager import def_function
  from tensorflow.python.framework import constant_op
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import test_util
  from tensorflow.python.ops import logging_ops
  from tensorflow.python.ops import sparse_ops
  from tensorflow.python.ops.ragged import ragged_factory_ops
  from tensorflow.python.ops.ragged import ragged_string_ops
  from tensorflow.python.ops.ragged import ragged_tensor
  from tensorflow.python.platform import googletest
label_desc: Use image node_id 3 for calling the RaggedToStringTest obj's underlying member method code with example usage: obj.testRaggedToStringUnknownRank() and returns: ragged_string_ops