fixed price drops/moved logging outside of init_monitor

tests/test_price_before_drop.py

@@ -0,0 +1,30 @@
+"""unit test: resolve_price_before_drop detects a drop from the prior stored price
+
+run from the repo root:
+    uv run python tests/test_price_before_drop.py
+
+pure and offline — no Mongo, no product construction; just the drop rule
+add_products_to_database relies on
+"""
+
+from monitor_utils.database import resolve_price_before_drop
+
+
+def test_drop_returns_previous_price():
+    """a strictly lower new price is a drop; the prior price is returned"""
+
+    assert resolve_price_before_drop(200.0, 150.0) == 200.0
+
+
+def test_non_drops_return_none():
+    """no prior price, an unchanged price, or a rise are not drops"""
+
+    assert resolve_price_before_drop(None, 150.0) is None  # new product
+    assert resolve_price_before_drop(150.0, 150.0) is None  # unchanged
+    assert resolve_price_before_drop(150.0, 200.0) is None  # price rose
+    assert resolve_price_before_drop(200.0, None) is None  # missing new price
+
+
+test_drop_returns_previous_price()
+test_non_drops_return_none()
+print("price before drop test passed")