diff --git a/tests/unit/test_docker_util_image.py b/tests/unit/test_docker_util_image.py
index 43c1922..a74196d 100644
--- a/tests/unit/test_docker_util_image.py
+++ b/tests/unit/test_docker_util_image.py
@@ -35,6 +35,8 @@ class TestImageCreatedAt(unittest.TestCase):
             return_value=_ok(stdout="2026-07-06T15:33:47.123456789Z\n"),
         ) as run:
             created = docker_mod.image_created_at("bot-bottle-claude:latest")
+        self.assertIsNotNone(created)
+        assert created is not None
         self.assertEqual(2026, created.year)
         self.assertEqual(123456, created.microsecond)
         self.assertEqual(timezone.utc, created.tzinfo)
diff --git a/tests/unit/test_macos_container_util.py b/tests/unit/test_macos_container_util.py
index 965117b..a0d3289 100644
--- a/tests/unit/test_macos_container_util.py
+++ b/tests/unit/test_macos_container_util.py
@@ -338,6 +338,8 @@ class TestMacosContainerImageCreatedAt(unittest.TestCase):
         payload = '[{"created": "2025-06-01T12:00:00"}]'
         with patch.object(util.subprocess, "run", return_value=self._ok(payload)):
             dt = util.image_created_at("bot-bottle-agent:latest")
+        self.assertIsNotNone(dt)
+        assert dt is not None
         self.assertEqual(2025, dt.year)
         self.assertEqual(6, dt.month)
         self.assertEqual(1, dt.day)
@@ -347,12 +349,16 @@ class TestMacosContainerImageCreatedAt(unittest.TestCase):
         payload = '[{"created": "2024-01-15T08:30:00"}]'
         with patch.object(util.subprocess, "run", return_value=self._ok(payload)):
             dt = util.image_created_at("some-image:latest")
+        self.assertIsNotNone(dt)
+        assert dt is not None
         self.assertEqual(2024, dt.year)
 
     def test_accepts_uppercase_Created_field(self):
         payload = '[{"Created": "2024-03-20T10:00:00"}]'
         with patch.object(util.subprocess, "run", return_value=self._ok(payload)):
             dt = util.image_created_at("some-image:latest")
+        self.assertIsNotNone(dt)
+        assert dt is not None
         self.assertEqual(2024, dt.year)
         self.assertEqual(3, dt.month)