code: def test_always_returns_none(self):
      f = once.once(lambda: "Hello, world!")
      with self.assertRaisesRegex(
          ValueError, "snt.once .* cannot return"
      ):
          f()
  
imports: import pickle
  from absl.testing import absltest
  from absl.testing import parameterized
  from sonnet.src import once
label_desc: Use image node_id 2 for calling the OnceTest obj's underlying member method code with example usage: obj.test_always_returns_none() without return types