US02-03: Execute Jobs with Leases, Locks, and Recovery (#56)

tests/unit/test_lock_order.py

@@ -0,0 +1,28 @@
+"""Lock acquisition ordering (deadlock prevention)."""
+
+import pytest
+
+from photo_pipeline.jobs import locks
+
+
+def test_broad_to_narrow_ranks():
+    assert locks.rank("library") < locks.rank("rename")
+    assert locks.rank("rename") < locks.rank("album")
+    assert locks.rank("album") < locks.rank("asset")
+
+
+def test_acquiring_narrower_while_holding_broader_is_allowed():
+    locks.validate_acquisition(["library"], "asset")  # no raise
+    locks.validate_acquisition(["library", "album"], "asset")
+
+
+def test_acquiring_broader_while_holding_narrower_is_rejected():
+    with pytest.raises(locks.LockOrderError):
+        locks.validate_acquisition(["asset"], "library")
+    with pytest.raises(locks.LockOrderError):
+        locks.validate_acquisition(["album"], "rename")
+
+
+def test_unknown_lock_is_rejected():
+    with pytest.raises(locks.LockOrderError):
+        locks.rank("nonsense")