I use it (and similar tech) because I don't want to think about individual boxes at scale, rather instances of an application. Containers + orchestration allow me to develop and test in the exact same environment my apps will be in in prod, which allows me to mostly remove the hardware and OS as a variable that could affect its runtime behavior. They also make it easier to spin up a local copy of my services' runtime environments for testing, as I need only describe it in a simple yaml file and spin it up w/ docker-compose in a single command.

I found at first testing was arduous, but you learn to adapt. In my case, I increased the amount of debug logs my application throws (can also be useful to enable in prod when trying to hunt down an issue) and invested time in creating unit/integration tests that run outside of the container/lambda to validate specific paths/features. Worst case there's always docker exec and language-specific debugging when I want to dig in manually.

I'm still pretty skeptical about serverless (I mostly use it for cloud-specific automation), but as much as people like to shit on Docker it's been pretty great to use from an ops perspective. I interpret most negativity about it as curmudgeonly reactions to the admittedly excessive hype in the technologies, with some fairly pedantic complaints about the (imo minimal) overhead such technologies incur thrown in as an uninteresting justification.

Posted an answer to another similar question: https://news.ycombinator.com/item?id=24250329 hope it helps when developing with your IDE :)