There are 2 environments for Paychoice. A production (secure) and a sandbox environment. The sandbox is specifically for testing and will not transact any real world money.
You can easily test how your application handles different scenarios from Paychoice by changing the cents value of the transaction to the appropriate error code. A complete list of error codes is available on our website at http://www.paychoice.com.au/docs/api/credit-card-error-codes/