code: def test_pareto_front() -> None:
      study = optuna.multi_objective.create_study(
          ["minimize", "maximize"]
      )
      assert {
          tuple(t.values) for t in study.get_pareto_front_trials()
      } == set()
  
      study.optimize(lambda t: [2, 2], n_trials=1)
      assert {
          tuple(t.values) for t in study.get_pareto_front_trials()
      } == {(2, 2)}
  
      study.optimize(lambda t: [1, 1], n_trials=1)
      assert {
          tuple(t.values) for t in study.get_pareto_front_trials()
      } == {(1, 1), (2, 2)}
  
      study.optimize(lambda t: [3, 1], n_trials=1)
      assert {
          tuple(t.values) for t in study.get_pareto_front_trials()
      } == {(1, 1), (2, 2)}
  
      study.optimize(lambda t: [1, 3], n_trials=1)
      assert {
          tuple(t.values) for t in study.get_pareto_front_trials()
      } == {(1, 3)}
      assert len(study.get_pareto_front_trials()) == 1
  
      study.optimize(
          lambda t: [1, 3], n_trials=1
      )  # The trial result is the same as the above one.
      assert {
          tuple(t.values) for t in study.get_pareto_front_trials()
      } == {(1, 3)}
      assert len(study.get_pareto_front_trials()) == 2
  
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 4 for calling a global function with example usage: test_pareto_front() without return types