The myPOS Web Checkout test environment is a self-contained testing environment. Once you are ready with the integration, you need to use it in order to make the appropriate tests of all your API calls and communication with the system. The test environment will let you test the API integration without affecting any real myPOS users or their real myPOS accounts.
The myPOS Web Checkout test environment mimics myPOS' production servers, so you can format and make all your calls to the system as you will do in production environment. The only difference between the calls on both environments is that you need to use different user credentials and endpoints.
Before you start using myPOS Web Checkout into production, you should test the application with all of the proposed case scenarios in test environment.