code: def testMergeDescriptorSingleString(self):
      p1 = Pool()
      p1.set("string", "1")
      p2 = Pool()
      p2.set("string", "2")
      # single value descriptors only allow for replace when merging data:
      self.assertRaises(
          EssentiaException, p1.mergeSingle, "string", p2["string"]
      )
      p1.mergeSingle("string", p2["string"], "replace")
      self.assertEqual(p1["string"], p2["string"])
  
imports: from essentia_test import *
label_desc: Use image node_id 34 for calling the TestPool obj's underlying member method code with example usage: obj.testMergeDescriptorSingleString() without return types