If it's decoupled, it's plenty testable. Serverless covers 2 scenarios very well: when you have volume so low, that you don't want to pay for reserved capacity

If it's decoupled, it's plenty testable. Serverless covers 2 scenarios very well: when you have volume so low, that you don't want to pay for reserved capacity: if nobody is using the stuff, you pay next to nothing. And also if there is a lot of load, it's very very easy to scale it to cover very high demand.