A developer is building an API to support a shopping cart application. The application ' s backend is an AWS Lambda function that integrates with Amazon API Gateway. The developer wants to have the ability to test new versions of the application in a development environment before pushing changes to production. The developer needs to test the application by using mock endpoints for external payment processor APIs. The tests must allow quality assurance (QA) testers to make calls against a separate development stage without impacting the production environment. When the tests are finished, the developer needs to publish new Lambda code safely and must have the option to perform rollbacks if issues occur. Which solution will meet these requirements in the MOST secure way?