message: Fix cluster_resolver test breakage in strategy_common_test.
diff: @@ -160,20 +160,16 @@ class StrategyClusterResolverTest(test.TestCase, parameterized.TestCase):
  with strategy.scope():
  self.assertIs(strategy.cluster_resolver, resolver)
  +
  self.assertTrue(hasattr(resolver, 'cluster_spec'))
  - if isinstance(strategy, TPUStrategy):
  - self.skipTest('b/159747888')
  - self.assertTrue(hasattr(resolver, 'environment'))
  self.assertTrue(hasattr(resolver, 'master'))
  self.assertTrue(hasattr(resolver, 'num_accelerators'))
  - self.assertIsNone(resolver.rpc_layer)
  + self.assertTrue(hasattr(resolver, 'task_id'))
  + self.assertTrue(hasattr(resolver, 'task_type'))
  if isinstance(strategy, CollectiveAllReduceStrategy):
  self.assertEqual(resolver.task_id, 0)
  self.assertAllInSet(resolver.task_type, ['chief', 'worker'])
  - elif isinstance(strategy, TPUStrategy):
  - # TPUStrategy does not have task_id and task_type applicable.
  - self.assertIsNone(resolver.task_id)
  - self.assertIsNone(resolver.task_type)
  + self.assertIsNone(resolver.rpc_layer)
  if __name__ == '__main__':
  