How to do in-app chaos testing

Relax! I'm not here to break your software. But I am here to show you how you can break the software you develop without changing the actual code!
Now, I hear you thinking: "Why on Earth should I do this? I have unit/integration/... tests"

Ah, yes, you have tests. Tell me, do you test what happens if a third-party service goes down? Or takes a lot longer to respond when that service hits its busiest time of the day?
Or what would happen if you tried to write data into a SQL database that has no more disk space?

All of these - and more! - cases can be discovered early, during development time. And I'll gladly show you how.