diff --git a/tests/test_pipeline_manifest.py b/tests/test_pipeline_manifest.py
index 44d9a2c..bb19e07 100644
--- a/tests/test_pipeline_manifest.py
+++ b/tests/test_pipeline_manifest.py
@@ -33,3 +33,15 @@ def test_rebuild_ring_edges_one_transition_per_edge_with_wrap():
         "transitions/orbit-abyss.mp4",
         "transitions/abyss-cosmos.mp4",     # wrap edge
     ]
+
+
+def test_add_ring_scale_appends_when_after_missing():
+    m = _base()
+    m = add_ring_scale(m, "abyss", "abyss", after="nope")
+    assert [s["id"] for s in m["ring"]["scales"]] == ["cosmos", "abyss"]
+
+
+def test_rebuild_ring_edges_single_scale_self_wrap():
+    m = _base()                       # one scale: cosmos
+    m = rebuild_ring_edges(m)
+    assert [t["file"] for t in m["ring"]["transitions"]] == ["transitions/cosmos-cosmos.mp4"]