code: def test_stack_feature_labels(self):
      sc = OrcaContext.get_spark_context()
      data = sc.parallelize(
          [(1, 2), (3, 4), (5, 6), (7, 8), (9, 10), (11, 12)]
      )
      repart1 = data.repartition(2)
      stacked1 = SparkXShards(repart1).stack_feature_labels().collect()
  
      repart2 = data.repartition(4)
      stacked2 = SparkXShards(repart2).stack_feature_labels().collect()
      assert len(stacked1) == 2
      assert len(stacked2) == 4
  
imports: import os.path
  import pytest
  from unittest import TestCase
  import bigdl.orca.data
  import bigdl.orca.data.pandas
  from bigdl.orca.data import SharedValue
  from bigdl.dllib.nncontext import *
  from bigdl.orca.data.transformer import *
  from bigdl.orca import init_orca_context
label_desc: Use image node_id 29 for calling the TestSparkXShards obj's underlying member method code with example usage: obj.test_stack_feature_labels() without return types