Android :: Android Market / Applications Can Be Downloaded Without Publishing?

Suppose you upload a paid app and you want to test if it works correctly when downloaded from Android Market - do you pay for it? Are your own apps free to you? And to download it from the market, do you have to make it visible to the whole world? I tried to upload an app, the uploader accepts it, but when I try to download it from the phone it says "package file was not signed correctly".

It's unacceptable that the uploader checks to see if a file is signed, but it somehow performs *Different* tests than what the phone actually does when it downloads apps. I hope I can debug this further without having to publish my app to test it and make my app momentarily visible to everybody.