USPS recommends testing their API with test tracking numbers but doesn't provide any. How can the USPS API be tested without valid testing tracking numbers.
I've been looking for USPS tracking API test tracking numbers to see USPS tracking API responses with different situation (eg, shipment delayed, or shipment signed off by [name], shipment returned to sender, etc).
I've looked everywhere I can think of, including USPS website, several years of USPS API documentation (near useless; can provide links on request), I've called USPS customer service for the API, and I've looked on SO/Google, to no avail.
I've run into this FedEx Tracking Number Question as well as this SO question for UPS test tracking numbers.