QUESTION:
What is the significance of the Test Mode checkbox if I am already connecting to the Moneris test environment using test ID for the StoreID and CheckoutID?  Can I use this check box with my production store that I set up in  https://www3.moneris.com/mpg to test that as well?

ANSWER:
Test Mode cannot be used with Production credentials
In order to use Test Mode, you will have to connect to the Moneris QA environment and create a new Moneris Checkout Profile:

Username: demouser
Store: store3
(This is the most full-featured store as it includes support for Gift Card testing)
Password: password
Please review this link for instructions on testing a solution:


Moneris Checkout Credentials:
StoreID: store3
API Key: yesguy
CheckoutID: chktSM98Btore2