What do you mean by testing an address? Why would you need to "test" it?
It has been speculated by many that MtGox lost the private keys to their cold cold storage wallets because of a bug in their key generation software.
Before putting 10,000 BTC in an address, I would want to check to make sure the private key really works for that address. Wouldn't you?
In that case you can sign a message with the private key and use one of the many signature-validation-tools out there to validate the signature.