code: def test_da(self):
      a = dd.from_pandas(dummy, npartitions=2)
      de = dpp.DummyEncoder()
      result = de.fit_transform(a)
      assert isinstance(result, dd.DataFrame)
  
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 4 for calling the TestDummyEncoder obj's underlying member method code with example usage: obj.test_da() without return types