If you're booking the theory or practical driving test online, then your application will not go through. They usually ask you for your provisional driving licence number before you can even pick dates and make payment and if for any reason, your licence is invalid (eg banned from driving), then the system will refuse to let you continue with the booking. So you won't lose your money because validation of your licence occurs first.
If you were to send an application by post, they would return your money if your licence was invalid.
