diff --git a/package/samplers/auto_sampler/tests/test_sampler.py b/package/samplers/auto_sampler/tests/test_sampler.py
index 039c8fc8..470c47e4 100644
--- a/package/samplers/auto_sampler/tests/test_sampler.py
+++ b/package/samplers/auto_sampler/tests/test_sampler.py
@@ -6,6 +6,7 @@
 from multiprocessing.managers import DictProxy
 import os
 from typing import Any
+from unittest.mock import Mock
 import warnings
 
 from _pytest.fixtures import SubRequest
@@ -704,11 +705,17 @@ def test_cache_is_invalidated(
     n_jobs: int, relative_sampler_class: Callable[[], BaseSampler]
 ) -> None:
     sampler = relative_sampler_class()
+    original_before_trial = sampler.before_trial
+
+    def mock_before_trial(study: Study, trial: FrozenTrial) -> None:
+        assert study._thread_local.cached_all_trials is None
+        original_before_trial(study, trial)
+
+    sampler.before_trial = Mock(side_effect=mock_before_trial)
     study = optuna.study.create_study(sampler=sampler)
 
     def objective(trial: Trial) -> float:
         assert trial._relative_params is None
-        assert study._thread_local.cached_all_trials is None
 
         trial.suggest_float("x", -10, 10)
         trial.suggest_float("y", -10, 10)