Payment gateways are one of today's most important integrations that are done in the ever trending online market space. Any online market space that requires a transaction needs a payment gateway, be it Amazon, Flipkart, Uber, Airbnb, MakeMyTrip, Big Basket, etc.
Integration testing remains a mystery for an application with a payment gateway. I say so because most of us usually do not unveil the actual testing efforts required to test the gateway integration. We have a tendency to ensure payments happen with a valid card, and it does not happen with an invalid card. But trust me, it's much more than that.