code: def test_mock_multiple_data_source():
      with tfds.testing.mock_data(num_examples=10):
          imagenet = tfds.data_source("imagenet2012", split="train")
          librispeech = tfds.data_source(
              "librispeech_lm", split="train"
          )
  
          # Data sources of different element specs produce different elements.
          assert set(next(iter(imagenet)).keys()) != set(
              next(iter(librispeech)).keys()
          )
  
imports: import functools
  import pickle
  import numpy
  import pytest
  import tensorflow
  import tensorflow_datasets
label_desc: Use image node_id 20 for calling a global function with example usage: test_mock_multiple_data_source() without return types