You can't "test" the module by using generic credentials. You'll need to get an actual account and supply the username+key before the module will be able to process a transaction for you, even in test mode. (Test mode just means that it doesn't actually charge the card, only simulates it ... but still must have a real Authnet account to do so.)

Related FAQ: https://www.zen-cart.com/tutorials/i...hp?article=373
And if you need an account: http://www.zen-cart.com/index.php?ma...es&pages_id=45