code: def test_astype_categorical(self, dtype):
      # GH#18099
      d = {"A": list("abbc"), "B": list("bccd"), "C": list("cdde")}
      df = DataFrame(d)
      result = df.astype(dtype)
      expected = DataFrame(
          {k: Categorical(v, dtype=dtype) for k, v in d.items()}
      )
      tm.assert_frame_equal(result, expected)
  
imports: import re
  import numpy
  import pytest
  import pandas.util._test_decorators
  import pandas
  from pandas import Categorical, CategoricalDtype, DataFrame, DatetimeTZDtype, Index, Interval, IntervalDtype, NaT, Series, Timedelta, Timestamp, concat, date_range, option_context
  import pandas._testing
label_desc: Use image node_id 13 for calling the TestAstype obj's underlying member method code with example usage: obj.test_astype_categorical(dtype) without return types