code: def test_set_dtype_new_categories(self):
      c = Categorical(["a", "b", "c"])
      result = c._set_dtype(CategoricalDtype(list("abcd")))
      tm.assert_numpy_array_equal(result.codes, c.codes)
      tm.assert_index_equal(
          result.dtype.categories, Index(list("abcd"))
      )
  
file_path: pandas/pandas/tests/arrays/categorical/test_dtypes.py
imports: import numpy
  import pytest
  from pandas.core.dtypes.dtypes import CategoricalDtype
  from pandas import Categorical, CategoricalIndex, Index, IntervalIndex, Series, Timestamp
  import pandas._testing
label_desc: Use image node_id 3 for calling the TestCategoricalDtypes obj's underlying member method code with example usage: obj.test_set_dtype_new_categories() without return types