"""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")