diff --git a/python_tests/test_api.py b/python_tests/test_api.py
index ae50e29a..c0304a37 100644
--- a/python_tests/test_api.py
+++ b/python_tests/test_api.py
@@ -102,7 +102,7 @@ class APITestCase(TestCase):
 
     def test_get_best_trials_of_preferential_study(self) -> None:
         storage = optuna.storages.InMemoryStorage()
-        study = create_study(storage=storage)
+        study = create_study(n_generate=4, storage=storage)
         for _ in range(3):
             trial = study.ask()
             study.mark_comparison_ready(trial)
@@ -125,7 +125,7 @@ class APITestCase(TestCase):
 
     def test_report_preference(self) -> None:
         storage = optuna.storages.InMemoryStorage()
-        study = create_study(storage=storage)
+        study = create_study(n_generate=4, storage=storage)
         for _ in range(3):
             trial = study.ask()
             study.mark_comparison_ready(trial)
@@ -153,7 +153,7 @@ class APITestCase(TestCase):
 
     def test_skip_trial(self) -> None:
         storage = optuna.storages.InMemoryStorage()
-        study = create_study(storage=storage)
+        study = create_study(n_generate=4, storage=storage)
         trials: list[optuna.Trial] = []
         for _ in range(3):
             trial = study.ask()