Test labels are a great way to see what a USPS label will look like when you print it, without having to purchase the postage required for a valid label. Currently, you can create test labels when using either Stamps.com or Express 1 as your postage provider.
*UPS and FedEx do not support the creation of test labels since you are invoiced for labels only when they are used.
Note: in order to create a USPS test label, you will need to have a balance on your postage provider account. You can check this (and add funds if necessary) by going to Settings > Shipping > Carriers & Fulfillment.
Create a test label
Select one of your orders, make sure that it has the correct carrier, method, and rate, and click the Create Label button.
Now, check the box next to Create a test label, and then click Create Label.
When you create a test label, it will use the shipping settings you set for that order, but it won't do anything to that order. Meaning, the marketplace and/or customer will not be notified, you will not be charged for the label, nor will the order be marked as shipped or a shipment record created. You can create and print the label just as you would normally, and the label will look exactly as it would were it a real shipment but with the word Sample across it.
Just remember that the order has not been altered, so you will need to create a "real" shipment when you are ready to ship that order.
NOTE: Currently, test labels are supported only in US-based accounts and with USPS labels.