You have state even in functional programs. My original point was about simplifying the program so it is easier to reason about in the first place, rather than

You have state even in functional programs. My original point was about simplifying the program so it is easier to reason about in the first place, rather than write tests for a yet-to-be-overengineered-mess :) What if you get very tight memory/cpu constraints and FP/immutability isn't available/affordable? What if your programs runs on millions of networked nodes simultaneously? GUIs are still very stateful even with FP for one! So if you're going to write property-based tests after you know what the properties of the system are, and these will cover way, way more cases than you'll ever think of writing tests for manually, why even bother? What I do see is people deluding themselves into thinking their software is reliable when it definitely isn't and they're now even less careful when developing because they've got tests to protect them.