People get too hung up on the question "to test or not to test" instead of asking the question "where and when should I test". I started my career writing iOS

People get too hung up on the question "to test or not to test" instead of asking the question "where and when should I test". I started my career writing iOS clients, and the obsession with TDD was baffling. 80% of my code was usually either UI or simple Core Data manipulations, while the last 20% was mostly API parsing and a touch of business logic. I wrote a few tests for parsing corner cases or business logic, but they never really gave me any confidence or helped with refactoring, instead taking up time and adding overhead whenever I made changes. I supposed I didn't have enough coverage to get the benefits, but what tests would I write for my UI? What tests would I write for simple Core Data queries (which is assuredly unit tested already)? What tests would I write for my parsing libraries (which are already unit tested)? Then I started working on the (Python + Flask) API backend, and tests were self-evidently necessary. Python is dynamically typed, which can result in lots of corner cases when doing simple data manipulations. Python is interpreted, which means the compiler/IDE won't warn you about syntax issues without running the code, and you can't catch even the simplest logic errors without running the function. Most importantly, the API's entire job is translating data, inputs are in the API parameters or database, and output is the JSON. It's a perfect function, and tests were obvious. I wrote something like 600 in a week, then used them to make some major refactors with confidence. What I learned from those juxtapositions was that unit tests and automation are invaluable in certain circumstances. Specifically _any system that creates machine-readable output_ like JSON, populating a database, or even a non-trivial object factory should be unit tested like crazy. Any system that creates human-readable output, like views or changes in an unreachable database (something like an external API or a bank account) needs to be human-tested, there's just no way around it.