code: def test_reindex(self):
      self.grouping.reindex(self.grouping.index)
  
imports: from statsmodels.compat.pandas import assert_frame_equal, assert_series_equal
  import numpy
  from numpy.testing import assert_equal
  import pandas
  import pytest
  from scipy import sparse
  from statsmodels.tools.grouputils import dummy_sparse, Grouping, Group, combine_indices, group_sums
  from statsmodels.datasets import grunfeld, anes96
label_desc: Use image node_id 1 for calling the CheckGrouping obj's underlying member method code with example usage: obj.test_reindex() without return types