How do I test my WhatsApp messages without bothering real customers?

Order from yourself. Open your own page, add a small item, and check out with your own name and WhatsApp number. The confirmation arrives on your phone, the ticket lands in your managers group and the dispatch in your riders group, exactly as a customer would see them. Move the order along on the orders board and watch each update arrive. Then open Reports → Message history and read the rows: sent, or failed with the reason in plain English. Cancel the test order from the board afterwards, which puts any counted stock back. Nothing about a test order reaches anyone but you and your groups.