code: def testChangedField(self):
      a = sc_pb.ResponseObservation(
          observation=sc_pb.Observation(game_loop=1)
      )
      b = sc_pb.ResponseObservation(
          observation=sc_pb.Observation(game_loop=2)
      )
      diff = proto_diff.compute_diff(a, b)
      self.assertIsNotNone(diff)
      self.assertLen(diff.changed, 1, diff)
      self.assertEqual(str(diff.changed[0]), "observation.game_loop")
      self.assertEqual(diff.changed, diff.all_diffs())
      self.assertEqual(
          diff.report(), "Changed observation.game_loop: 1 -> 2."
      )
  
imports: from absl.testing import absltest
  from pysc2.lib import proto_diff
  from s2clientprotocol import sc2api_pb2
  from s2clientprotocol import score_pb2
label_desc: Use image node_id 6 for calling the ProtoDiffTest obj's underlying member method code with example usage: obj.testChangedField() without return types