code: def test_callbacks() -> None:
      study = optuna.multi_objective.create_study(
          ["minimize", "maximize"]
      )
  
      def objective(
          trial: optuna.multi_objective.trial.MultiObjectiveTrial,
      ) -> Tuple[float, float]:
          x = trial.suggest_float("x", 0, 10)
          y = trial.suggest_float("y", 0, 10)
          return x, y
  
      list0 = []
      list1 = []
      callbacks = [
          lambda study, trial: list0.append(trial.number),
          lambda study, trial: list1.append(trial.number),
      ]
      study.optimize(objective, n_trials=2, callbacks=callbacks)
  
      assert list0 == [0, 1]
      assert list1 == [0, 1]
  
file_path: optuna/tests/multi_objective_tests/test_study.py
imports: from typing import List
  from typing import Tuple
  import uuid
  import _pytest.capture
  import pytest
  import optuna
  from optuna.study._study_direction import StudyDirection
  from optuna.testing.storages import StorageSupplier
label_desc: Use image node_id 7 for calling a global function with example usage: test_callbacks() and returns: x,  y