def test_update_stock(inventory_fixture, ingredient_cost_fixture):
system1 = System(inventory_fixture, ingredient_cost_fixture)
orig_white_buns = system1.Inventory["white"]
system1.Update_Stock("white", 5)
assert (system1._Inventory["white"] == (orig_white_buns + 5))
system1.Update_Stock("white", -10)
assert (system1._Inventory["white"] == (orig_white_buns - 5))
