class_docstr: Test case which handles TPU hard placement.
class_docstr_tok: ["Test","case","which","handles","TPU","hard","placement","."]
code: def primary_device(self):
      if "TPU" in self._device_types:
          return "TPU"
      elif "GPU" in self._device_types:
          return "GPU"
      else:
          return "CPU"
  
imports: import functools
  import inspect
  import itertools
  import os
  import sys
  import threading
  import types
  from typing import Sequence, Tuple, Type, TypeVar
  from absl.testing import parameterized
  import tensorflow
label_desc: Use image node_id 3 for calling the TestCase obj's underlying member method code with example usage: obj.primary_device() and returns: str, str, str