Here ARRrr a few test labels that were created with Pirate Ship, which you can use to verify that your printer is working correctly:
USPS® test labels
One 2x7" label, used for Dymo 450 / Brother QL-800 printers: Download the PDF file here
Two 4x6” labels in a letter-size 8.5x11” paper, used for regular desktop printers: Download the PDF file here
One 4x6" label on a letter-size 8.5x11" paper: Download the PDF file here
One 4x6” label, used for label printers: Download the PDF file here
One 4x6" label in ZPL format: Download the ZPL file here
4x6" and 2x7" labels: USPS offers postage in both the 4x6" and 2x7" sizes.
UPS® test labels
Two 4x6" labels in a letter-size 8.5x11” paper, used for regular desktop printers: Download the PDF file here
One 4x6" label on a letter-size 8.5x11" paper: Download the PDF file here
One 4x6" label, used for label printers: Download the PDF file here
One 4x6" label in ZPL format: Download the ZPL file here
4x6" labels only: UPS labels only come in the standard 4x6" size, and not 2x7".
Additional resources