code: def test_getitem(self):
      with self.assertRaises(NotImplementedError):
          self.av[:1]
  
imports: import unittest
  import chainer
  import chainer.functions
  from chainer import testing
  import numpy
  from chainerrl import action_value
label_desc: Use image node_id 7 for calling the TestSingleActionValue obj's underlying member method code with example usage: obj.test_getitem() without return types