code: def testSmallCapacityConstructor(self):
      tree = sum_tree.SumTree(capacity=1)
      self.assertEqual(len(tree.nodes), 1)
      tree = sum_tree.SumTree(capacity=2)
      self.assertEqual(len(tree.nodes), 2)
  
imports: import random
  import unittest
  from reagent.replay_memory import sum_tree
label_desc: Use image node_id 4 for calling the SumTreeTest obj's underlying member method code with example usage: obj.testSmallCapacityConstructor() without return types