code: def testConcat(self):
      components = np.array(list("abcdefghijklmnopqrst")).view(
          np.chararray
      )
      reducer = grouping.Reducer(
          init_func=lambda x: "",
          reduce_func=lambda x, y: x + y[0],
          finalize_func=lambda x: x,
      )
      for i in range(1, 11):
          dataset = dataset_ops.Dataset.zip(
              (
                  dataset_ops.Dataset.from_tensor_slices(components),
                  dataset_ops.Dataset.range(2 * i),
              )
          ).apply(
              grouping.group_by_reducer(lambda x, y: y % 2, reducer)
          )
          self.assertDatasetProduces(
              dataset,
              expected_shapes=tensor_shape.TensorShape([]),
              expected_output=[b"acegikmoqs"[:i], b"bdfhjlnprt"[:i]],
          )
  
imports: from absl.testing import parameterized
  import numpy
  from tensorflow.python.data.experimental.ops import grouping
  from tensorflow.python.data.kernel_tests import checkpoint_test_base
  from tensorflow.python.data.kernel_tests import test_base
  from tensorflow.python.data.ops import dataset_ops
  from tensorflow.python.framework import combinations
  from tensorflow.python.framework import constant_op
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import errors
  from tensorflow.python.framework import sparse_tensor
  from tensorflow.python.framework import tensor_shape
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import math_ops
  from tensorflow.python.platform import test
label_desc: Use image node_id 3 for calling the GroupByReducerTest obj's underlying member method code with example usage: obj.testConcat() without return types