class_docstr: Test class for preprocessing tests.
code: def test_scaling(self):
      yield self.check_scaling_features, False, False
      yield self.check_scaling_features, False, True
      yield self.check_scaling_features, True, False
      yield self.check_scaling_features, True, True
  
imports: import json
  import os
  import re
  import unittest
  import numpy
  import scipy.sparse
  from numpy.testing import assert_almost_equal, assert_array_equal
  from sklearn.datasets import make_classification
  from sklearn.feature_extraction import FeatureHasher
  from skll.data import FeatureSet, NDJWriter
  from skll.experiments import run_configuration
  from skll.learner import Learner
  from skll.learner.utils import SelectByMinCount
  from skll.utils.testing import config_dir, fill_in_config_paths, output_dir, test_dir, train_dir, unlink
label_desc: Use image node_id 9 for calling the TestPreprocessing obj's underlying member method code with example usage: obj.test_scaling() without return types