code: def testSampleSingleton(self):
      self._tree.set(node_index=5, value=1.0)
      item = self._tree.sample()
  
      self.assertEqual(item, 5)
  
imports: import random
  import unittest
  from reagent.replay_memory import sum_tree
label_desc: Use image node_id 10 for calling the SumTreeTest obj's underlying member method code with example usage: obj.testSampleSingleton() without return types