code: def testUnpackPackRoundTrip(self):
      opt_init, _, _ = optimizers.momentum(0.1, mass=0.9)
      params = [
          {"w": self.rng().randn(1, 2), "bias": self.rng().randn(2)}
      ]
      expected = opt_init(params)
      ans = optimizers.pack_optimizer_state(
          optimizers.unpack_optimizer_state(expected)
      )
      self.assertEqual(ans, expected)
  
imports: import functools
  from absl.testing import absltest
  import numpy
  import jax.numpy
  import jax._src.test_util
  from jax import jit, grad, jacfwd, jacrev
  from jax import tree_util
  from jax import lax
  from jax.example_libraries import optimizers
  from jax import config
label_desc: Use image node_id 27 for calling the OptimizerTests obj's underlying member method code with example usage: obj.testUnpackPackRoundTrip() without return types