I write both client-side and server-side code. In server-side, almost all code is atomic, very functional and is very easy to cover with tests, on different le

I write both client-side and server-side code. In server-side, almost all code is atomic, very functional and is very easy to cover with tests, on different levels. I start with several unit tests before implementation and then add a new test for any bug. The client, however, is a completely different story. It's a thick game client, and through my career I honestly tried adopting TDD for it - but the domain itself is very unwelcoming to this approach. The tests were very brittle, with a ton of time spend to set them up, and didn't catch any significant bugs. In the end, I abandoned trying to write tests for it altogether - at least I'll be able to write my own, functional and test-driven game engine, to begin with.