code: def test_remove_unused_categories(self):
      pidx = pd.CategoricalIndex([1, 4, 5, 3], categories=[4, 3, 2, 1])
      psidx = ps.from_pandas(pidx)
  
      self.assert_eq(
          pidx.remove_unused_categories(),
          psidx.remove_unused_categories(),
      )
  
imports: import unittest
  import pandas
  from pandas.api.types import CategoricalDtype
  import pyspark.pandas
  from pyspark.loose_version import LooseVersion
  from pyspark.testing.pandasutils import PandasOnSparkTestCase, TestUtils
label_desc: Use image node_id 5 for calling the CategoricalIndexTestsMixin obj's underlying member method code with example usage: obj.test_remove_unused_categories() without return types