code: def test_clf_head_get_sigmoid_postprocessor():
      head = head_module.ClassificationHead(name="a", multi_label=True)
      head._encoded = True
      head._encoded_for_sigmoid = True
      assert isinstance(
          head.get_hyper_preprocessors()[0].preprocessor,
          preprocessors.SigmoidPostprocessor,
      )
  
file_path: autokeras/autokeras/blocks/heads_test.py
imports: import keras_tuner
  import numpy
  import tensorflow
  from tensorflow import keras
  from tensorflow import nest
  import autokeras
  from autokeras import hyper_preprocessors
  from autokeras import nodes
  from autokeras import preprocessors
  from autokeras import test_utils
  from autokeras.blocks import heads
label_desc: Use image node_id 4 for calling a global function with example usage: test_clf_head_get_sigmoid_postprocessor() without return types