Yeah, coding like this ("pure" functions, input value -> output value, less/no side effects) is probably best "improved by just having unit tests. I'm not a TD

Yeah, coding like this ("pure" functions, input value -> output value, less/no side effects) is probably best "improved by just having unit tests. I'm not a TDD zealot, just that the unit test can provide the assurance of the computation, regardless of the spaghetti inside the computation.