One of the most transformative things I've come across for how to structure and test code has been Gary Bernhardt's talk on Boundaries [0]. I've watched it at least ten times. He also has an entire series on testing where he goes deeper into these ideas.
In this video, he talks of a concept called functional core, imperative shell. The functional core is your code that contains your core logic that can be easily unit tested because it just receives plain values from the outside world. The imperative shell is the outside world that talks to disks, databases, APIs, UIs, etc. and builds these values to be used in the core. I'll stop there—Gary's video will do 100x than I can do here :)
In this video, he talks of a concept called functional core, imperative shell. The functional core is your code that contains your core logic that can be easily unit tested because it just receives plain values from the outside world. The imperative shell is the outside world that talks to disks, databases, APIs, UIs, etc. and builds these values to be used in the core. I'll stop there—Gary's video will do 100x than I can do here :)
[0] https://www.destroyallsoftware.com/talks/boundaries