pos_display_total_quantity

Purpose

Display the total quantity of items in the POS order summary so cashiers can quickly verify that all articles were scanned.

Features

point_of_sale UI: Adds a total quantity line in the POS order summary showing the number of articles in the current order.
point_of_sale UI: Keeps the displayed total quantity in sync with order lines as products are added.
point_of_sale tests: Provides a POS web tour that checks the total quantity increases when the same product is added multiple times.