code: def test_runs_once(self):
      r = []
  
      @once.once
      def f():
          r.append(None)
  
      for _ in range(3):
          f()
  
      self.assertEqual(r, [None])
  
imports: import pickle
  from absl.testing import absltest
  from absl.testing import parameterized
  from sonnet.src import once
label_desc: Use image node_id 1 for calling the OnceTest obj's underlying member method code with example usage: obj.test_runs_once() without return types