code: def test_multi_label_loss():
      head = head_module.ClassificationHead(
          name="a", multi_label=True, num_classes=8, shape=(8,)
      )
      input_node = keras.Input(shape=(5,))
      output_node = head.build(
          keras_tuner.HyperParameters(), input_node
      )
      model = keras.Model(input_node, output_node)
      assert model.layers[-1].activation.__name__ == "sigmoid"
      assert head.loss.name == "binary_crossentropy"
  
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 3 for calling a global function with example usage: test_multi_label_loss() without return types