diff --git a/tests/tools/test_variation_checker.py b/tests/tools/test_variation_checker.py
new file mode 100644
index 00000000..ccb58eeb
--- /dev/null
+++ b/tests/tools/test_variation_checker.py
@@ -0,0 +1,57 @@
+from lib.variation_checker import check_scene_variation
+
+
+def _scene(scene_id: str, shot_size: str) -> dict:
+    return {
+        "id": scene_id,
+        "description": f"{scene_id} description",
+        "shot_intent": "support story beat",
+        "texture_keywords": ["texture"],
+        "shot_language": {
+            "shot_size": shot_size,
+            "camera_movement": "dolly_in",
+            "lighting_key": "soft",
+        },
+    }
+
+
+def test_non_consecutive_same_size_pairs_do_not_trigger_violation() -> None:
+    scenes = [
+        _scene("s1", "wide"),
+        _scene("s2", "wide"),
+        _scene("s3", "cu"),
+        _scene("s4", "cu"),
+        _scene("s5", "medium"),
+        _scene("s6", "medium"),
+    ]
+
+    result = check_scene_variation(scenes)
+
+    assert not any("consecutive same-size shots" in violation for violation in result["violations"])
+
+
+def test_true_run_of_three_same_size_shots_is_flagged() -> None:
+    scenes = [
+        _scene("s1", "wide"),
+        _scene("s2", "wide"),
+        _scene("s3", "wide"),
+        _scene("s4", "cu"),
+    ]
+
+    result = check_scene_variation(scenes)
+
+    assert "3 consecutive same-size shots. Vary shot sizes between scenes for editorial rhythm." in result["violations"]
+
+
+def test_unspecified_shots_do_not_extend_same_size_run() -> None:
+    scenes = [
+        _scene("s1", "wide"),
+        _scene("s2", "wide"),
+        _scene("s3", "unspecified"),
+        _scene("s4", "wide"),
+        _scene("s5", "wide"),
+    ]
+
+    result = check_scene_variation(scenes)
+
+    assert not any("consecutive same-size shots" in violation for violation in result["violations"])