diff --git a/python_tests/artifact/test_boto3.py b/python_tests/artifact/test_boto3.py
index 189a5bb2..1dc448f0 100644
--- a/python_tests/artifact/test_boto3.py
+++ b/python_tests/artifact/test_boto3.py
@@ -30,9 +30,9 @@ class Boto3BackendTestCase(TestCase):
 
         backend = Boto3Backend(self.bucket_name)
         backend.write(artifact_id, buf)
-        assert len(self.s3_client.list_objects(Bucket=self.bucket_name)["Contents"]) == 1
+        self.assertEqual(len(self.s3_client.list_objects(Bucket=self.bucket_name)["Contents"]), 1)
         obj = self.s3_client.get_object(Bucket=self.bucket_name, Key=artifact_id)
-        assert obj["Body"].read() == dummy_content
+        self.assertEqual(obj["Body"].read(), dummy_content)
 
         with backend.open(artifact_id) as f:
             actual = f.read()
@@ -44,11 +44,11 @@ class Boto3BackendTestCase(TestCase):
         backend = Boto3Backend(self.bucket_name)
         backend.write(artifact_id, io.BytesIO(b"Hello"))
         objects = self.s3_client.list_objects(Bucket=self.bucket_name)["Contents"]
-        assert len([obj for obj in objects if obj["Key"] == artifact_id]) == 1
+        self.assertEqual(len([obj for obj in objects if obj["Key"] == artifact_id]), 1)
 
         backend.remove(artifact_id)
         objects = self.s3_client.list_objects(Bucket=self.bucket_name).get("Contents", [])
-        assert len([obj for obj in objects if obj["Key"] == artifact_id]) == 0
+        self.assertEqual(len([obj for obj in objects if obj["Key"] == artifact_id]), 0)
 
     def test_file_not_found_exception(self) -> None:
         backend = Boto3Backend(self.bucket_name)
diff --git a/python_tests/test_cached_extra_study_property.py b/python_tests/test_cached_extra_study_property.py
index daa548bd..c02006a7 100644
--- a/python_tests/test_cached_extra_study_property.py
+++ b/python_tests/test_cached_extra_study_property.py
@@ -278,4 +278,4 @@ class _CachedExtraStudyPropertyUserAttrs(TestCase):
         cached_extra_study_property = _CachedExtraStudyProperty()
         cached_extra_study_property.update(trials)
         actual = {k: v for k, v in cached_extra_study_property.union_user_attrs}
-        assert actual == expected
+        self.assertEqual(actual, expected)
diff --git a/python_tests/test_form_widget.py b/python_tests/test_form_widget.py
index 5f474aa9..3ab35f5e 100644
--- a/python_tests/test_form_widget.py
+++ b/python_tests/test_form_widget.py
@@ -41,4 +41,4 @@ class FormWidgetsTestCase(TestCase):
             with self.subTest(f"{widget.__class__}-{i}"):
                 d = cast(Dict[str, Any], widget.to_dict())
                 restored = dict_to_form_widget(d)
-                assert widget == restored
+                self.assertEqual(widget, restored)
diff --git a/python_tests/test_metric_names.py b/python_tests/test_metric_names.py
index ca373809..32b00acc 100644
--- a/python_tests/test_metric_names.py
+++ b/python_tests/test_metric_names.py
@@ -21,4 +21,4 @@ class MetricNamesTestCase(unittest.TestCase):
         study_system_attrs = study._storage.get_study_system_attrs(study._study_id)
         metric_names = get_objective_names(study_system_attrs)
 
-        assert metric_names == ["val_loss", "flops"]
+        self.assertEqual(metric_names, ["val_loss", "flops"])
diff --git a/python_tests/test_note.py b/python_tests/test_note.py
index f37697dd..7cc02cd4 100644
--- a/python_tests/test_note.py
+++ b/python_tests/test_note.py
@@ -19,9 +19,9 @@ class NoteTestCase(TestCase):
         ]:
             with self.subTest(f"with_{dummy_body_str}_{attr_len}"):
                 attrs = note.split_body(dummy_body_str, None)
-                assert len(attrs) == attr_len
+                self.assertEqual(len(attrs), attr_len)
                 actual = note.concat_body(attrs, None)
-                assert dummy_body_str == actual
+                self.assertEqual(actual, dummy_body_str)
 
     def test_save_and_get_study_note(self) -> None:
         study = optuna.create_study()
@@ -32,11 +32,11 @@ class NoteTestCase(TestCase):
                 system_attrs = study._storage.get_study_system_attrs(study._study_id)
 
                 actual = get_note(study)
-                assert actual == body
+                self.assertEqual(actual, body)
 
                 note_dict = note.get_note_from_system_attrs(system_attrs, None)
-                assert note_dict["body"] == body
-                assert note_dict["version"] == expected_ver
+                self.assertEqual(note_dict["body"], body)
+                self.assertEqual(note_dict["version"], expected_ver)
 
     def test_save_and_get_trial_note(self) -> None:
         study = optuna.create_study()
@@ -48,8 +48,8 @@ class NoteTestCase(TestCase):
                 system_attrs = study._storage.get_study_system_attrs(study._study_id)
 
                 actual = get_note(trial)
-                assert actual == body
+                self.assertEqual(actual, body)
 
                 note_dict = note.get_note_from_system_attrs(system_attrs, trial._trial_id)
-                assert note_dict["body"] == body
-                assert note_dict["version"] == expected_ver
+                self.assertEqual(note_dict["body"], body)
+                self.assertEqual(note_dict["version"], expected_ver)