code: def _check_backends():
      """Check that all the backends were tested.
  
      This works by collecting all the test cases in globals() and verifying that
      they were rewritten correctly. We assume that after that point, the test
      system works.
      """
      tested_backends = set()
      for test_case in globals().values():
          if hasattr(test_case, "_BACKEND_TESTED"):
              tested_backends.add(test_case._BACKEND_TESTED)
  
      expected_backends = set(
          ["backend_numpy", "backend_jax", "backend_tensorflow"]
      )
      assert (
          tested_backends == expected_backends
      ), "Missing backends: {}".format(
          expected_backends - tested_backends
      )
      logging.info(
          "Tested Inference Gym backends: %s.",
          ", ".join(expected_backends),
      )
  
imports: import atexit
  import functools
  from absl import logging
  import jax
  import numpy
  import tensorflow.compat.v2
  import tensorflow.compat.v2
  import tensorflow_probability
  from tensorflow_probability.python.internal import test_util
  from inference_gym import targets
  from inference_gym.internal import test_util
label_desc: Use image node_id 1 for calling a global function with example usage: _check_backends() without return types