And yet in 2020, you still can't write an automated test suite that spins up a virgin test environment, simulates all relevant scenarios, and allows you to quickly verify that your integration is responding properly as part of your normal CI process.

Working with a single, persistent test environment that offers no facilities to manage events like simulated user actions, API requests and webhooks feels like programming in another, much less productive era. Sadly, this still seems to be the norm for online payment services.

It's particularly ironic that online payment services are among the worst offenders for making API changes that require significant changes to integrations or even a whole new integration, and that by their nature they are also at high risk of Very Bad Things happening if an integration breaks. This is exactly the sort of situation where you really want a tight feedback loop and ongoing automated integration testing! Stripe used to be a welcome exception, but even they have dropped the ball badly in recent times.