code: def testSnapshot(self, already_written):
      num_workers = 3
      cluster = data_service_test_base.TestCluster(
          num_workers=num_workers
      )
      ds = dataset_ops.Dataset.range(100)
      ds = ds.snapshot(self.get_temp_dir())
      if already_written:
          # Materialize the snapshot.
          self.getDatasetOutput(ds)
  
      ds = self._make_dynamic_sharding_dataset(ds, cluster)
      error_regex = "Splitting is not implemented for snapshot datasets"
      with self.assertRaisesRegex(
          errors.UnimplementedError, error_regex
      ):
          self.getDatasetOutput(ds)
  
imports: import collections
  from absl.testing import parameterized
  import numpy
  from tensorflow.python.data.experimental.kernel_tests.service import test_base
  from tensorflow.python.data.experimental.ops import data_service_ops
  from tensorflow.python.data.kernel_tests import test_base
  from tensorflow.python.data.kernel_tests import tf_record_test_base
  from tensorflow.python.data.ops import dataset_ops
  from tensorflow.python.data.ops import readers
  from tensorflow.python.framework import combinations
  from tensorflow.python.framework import errors
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import random_ops
  from tensorflow.python.platform import test
label_desc: Use image node_id 25 for calling the DynamicShardingTest obj's underlying member method code with example usage: obj.testSnapshot(already_written) without return types