docs: def load_target_from_cache(target: Target, build_context) -> (bool, bool):
      """Load `target` from build cache, restoring cached artifacts & summary.
         Return (build_cached, test_cached) tuple.
  
      `build_cached` is True if target restored successfully.
      `test_cached` is True if build is cached and test_time metadata is valid.
      """
      cache_dir = build_context.conf.get_cache_dir(target, build_context)
      if not isdir(cache_dir):
          logger.debug('No cache dir found for target {}', target.name)
          return False, False
      # read summary file and restore relevant fields into target
      with open(join(cache_dir, 'summary.json'), 'r') as summary_file:
          summary = json.loads(summary_file.read())
      for field in ('build_time', 'test_time', 'created', 'accessed'):
          target.summary[field] = summary.get(field)
      # compare artifacts hash
      if (hash_tree(join(cache_dir, 'artifacts.json')) !=
              summary.get('artifacts_hash', 'no hash')):
          return False, False
      # read cached artifacts metadata
      with open(join(cache_dir, 'artifacts.json'), 'r') as artifacts_meta_file:
          artifact_desc = json.loads(artifacts_meta_file.read())
      # restore all artifacts
      for type_name, artifact_list in artifact_desc.items():
          artifact_type = getattr(AT, type_name)
          for artifact in artifact_list:
              # restore artifact to its expected src path
              if artifact_type not in _NO_CACHE_TYPES:
                  if not restore_artifact(
                          artifact['src'], artifact['hash'], build_context.conf):
                      target.artifacts.reset()
                      return False, False
              if artifact_type in (AT.docker_image,):
                  # "restore" docker image from local registry
                  image_id = artifact['src']
                  image_full_name = artifact['dst']
                  try:
                      tag_docker_image(image_id, image_full_name)
                  except:
                      logger.debug('Docker image with ID {} not found locally',
                                   image_id)
                      target.artifacts.reset()
                      return False, False
                  target.image_id = image_id
              target.artifacts.add(
                  artifact_type, artifact['src'], artifact['dst'])
      write_summary(summary, cache_dir)
      # check that the testing cache exists.
      if not isfile(join(cache_dir, 'tested.json')):
          logger.debug('No testing cache found for target {}', target.name)
          return True, False
      # read the testing cache.
      with open(join(cache_dir, 'tested.json'), 'r') as tested_file:
          target.tested = json.loads(tested_file.read())
          test_key = target.test_hash(build_context)
          return True, (target.tested.get(test_key) is not None)