Adds test coverage to verify landed costs on incoming shipments, including cases where some stock has already been sold and where costs need to be reversed. This helps ensure inventory valuation and accounting entries remain accurate in more realistic purchasing scenarios.

Task: https://www.odoo.com/web?#id=19693&view_type=form&model=project.task&menu_id=3942&action=327
pad: https://pad.odoo.com/p/r.g8GNmviPc7vFEis3