code: def test_flatten_flax_to_haiku(self):
      variables = {
          "params": {"mod1": {"mod2": {"w": 0}}, "~": {"w": 1}}
      }
      hk_params = utils.flatten_flax_to_haiku(variables["params"])
      self.assertEqual(
          hk_params, {"mod1/mod2": {"w": 0}, "~": {"w": 1}}
      )
  
imports: from absl.testing import absltest
  from absl.testing import parameterized
  from haiku._src.flax import utils
label_desc: Use image node_id 1 for calling the UtilsTest obj's underlying member method code with example usage: obj.test_flatten_flax_to_haiku() without return types