Seriously, how do you TDD?
by rcd2 on Hacker News.
Although I understand its mantra, I was never able to “drive the design” using TDD. To highlight my issues, let me share a recent failed experiment. I have been trying to create a command line tool to categorise my expenses and show a total by category. I’ve been using this exercise to practice TDD. In my latest frustrated attempt, my first test was along the lines of “it can categorise a single transaction correctly”. The problem with this is that this is testing the “tip of the iceberg” that will be almost the whole, final app. I think I was attempting a more “top down” design strategy here. Before that one, I tried the opposite: a more “bottom up” approach. I know I need to, at least, read a CSV, parse a CSV row into some data structure and then categorise it. So I TDDed my way through to complete these “sub problems”. However, when I was about to apply the categorisation rules I realised that the data structure I created didn’t help, was just bad and didn’t work at all :). So, how do you do it when you have a “larger project” (here, “larger” means something that’s not your typical “2/3 points user story” at work)? I always end up feeling stuck whether I try bottom-up or top-down.