code: def test_idempotence(self):
      X = np.arange(100).reshape((25, 4))
      bt = BlockTransformer(lambda x: 2 * x)
      assert_estimator_equal(bt.fit(X), bt.fit(X).fit(X))
  
file_path: dask-ml/tests/preprocessing/test_block_transformer.py
imports: import dask
  import dask.array
  import dask.dataframe
  import numpy
  import pandas
  import pytest
  from dask_ml.preprocessing import BlockTransformer
  from dask_ml.utils import assert_estimator_equal
label_desc: Use image node_id 3 for calling the TestBlockTransformer obj's underlying member method code with example usage: obj.test_idempotence() without return types