I can't get Pinpoint test messaging to work

I am using Pinpoint to send push notifications to a mobile app.

I'd like to be able to test the notification before I send it. The test for is asking me to enter either an "Endpoint ID" or a "Device token". I don't know what either of these is, or where to find them. I have scoured the menus in Pinpoint expecting to see a list of one or the other, but I find no such list.

I know the UserID of the device I want to receive the notification, but that doesn't work.

How do I do this?