code: def test_astype_categoricaldtype(self):
      ser = Series(["a", "b", "a"])
      result = ser.astype(CategoricalDtype(["a", "b"], ordered=True))
      expected = Series(Categorical(["a", "b", "a"], ordered=True))
      tm.assert_series_equal(result, expected)
  
      result = ser.astype(CategoricalDtype(["a", "b"], ordered=False))
      expected = Series(Categorical(["a", "b", "a"], ordered=False))
      tm.assert_series_equal(result, expected)
  
      result = ser.astype(
          CategoricalDtype(["a", "b", "c"], ordered=False)
      )
      expected = Series(
          Categorical(
              ["a", "b", "a"], categories=["a", "b", "c"], ordered=False
          )
      )
      tm.assert_series_equal(result, expected)
      tm.assert_index_equal(
          result.cat.categories, Index(["a", "b", "c"])
      )
  
imports: from datetime import datetime, timedelta
  from importlib import reload
  import string
  import sys
  import numpy
  import pytest
  from pandas._libs.tslibs import iNaT
  import pandas.util._test_decorators
  from pandas import NA, Categorical, CategoricalDtype, DatetimeTZDtype, Index, Interval, NaT, Series, Timedelta, Timestamp, cut, date_range, to_datetime
  import pandas._testing
label_desc: Use image node_id 3 for calling the TestAstypeCategorical obj's underlying member method code with example usage: obj.test_astype_categoricaldtype() without return types