What are some less-known coding principles/patterns?

I'm a hobbyist game developer. I've seen lots of resources go over SOLID principles, DRY, etc., and I've used design patterns such as the strategy, listener, singleton, and factory patterns in my game projects. Unit testing wasn't something I really did for my games though. I wrote unit tests for full-stack projects, but I always assumed that the code in games were too coupled with the UI to be reliably tested with unit tests, so I didn't write unit tests for my