Adding tests to a large monolithic tightly coupled legacy application using non-trivial examples. I can never find a tutorial for testing that's not using trivial examples or code that's already pretty good and just needs tests.
Not exactly a step by step tutorial, but "Working Effectively with Legacy Code" by Michael Feathers is fantastic reference material for this.
Have it on my desk right now. :)
Setting up a web development environment in WSL. Node, NVM, Zsh, Docker, PHP.