code: def test_astype_category_to_extension_dtype(self, expected):
      # GH#28668
      result = expected.astype("category").astype(expected.dtype)
  
      tm.assert_extension_array_equal(result, expected)
  
file_path: pandas/pandas/tests/arrays/categorical/test_astype.py
imports: import numpy
  import pytest
  from pandas import Categorical, CategoricalDtype, CategoricalIndex, DatetimeIndex, Interval, NaT, Period, Timestamp, array, to_datetime
  import pandas._testing
label_desc: Use image node_id 2 for calling the TestAstype obj's underlying member method code with example usage: obj.test_astype_category_to_extension_dtype(expected) without return types