code: def test_dask(self):
      a = dd.from_pandas(raw, npartitions=2)
      ce = dpp.Categorizer()
      trn = ce.fit_transform(a)
      assert is_categorical_dtype(trn["A"])
      assert is_categorical_dtype(trn["B"])
      assert is_categorical_dtype(trn["C"])
      assert trn["D"].dtype == np.dtype("int64")
      tm.assert_index_equal(ce.columns_, pd.Index(["A", "B", "C"]))
  
imports: from copy import copy
  import dask
  import dask.array
  import dask.dataframe
  import numpy
  import pandas
  import pandas.testing
  import pytest
  import sklearn.preprocessing
  from dask import compute
  from dask.array.utils import assert_eq
  from dask.dataframe.utils import assert_eq
  from pandas.api.types import is_categorical_dtype, is_object_dtype
  from sklearn.exceptions import NotFittedError
  import dask_ml.preprocessing
  from dask_ml.datasets import make_classification
  from dask_ml.utils import assert_estimator_equal
label_desc: Use image node_id 3 for calling the TestCategorizer obj's underlying member method code with example usage: obj.test_dask() without return types