code: def testFunction(self):
      def f(x):
          return x
  
      hparams = hparam.HParams(function=f)
      self.assertEqual(hparams.function, f)
  
      json_str = hparams.to_json()
      self.assertEqual(json_str, "{}")
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from tensor2tensor.utils import hparam
  import tensorflow.compat.v1
label_desc: Use image node_id 6 for calling the HParamsTest obj's underlying member method code with example usage: obj.testFunction() and returns: x