[dataduck]

So how do you test the design? I ask this sincerely. To me it seems that it's rare to know in correct detail what the design is supposed to do in advance, but also that even if you do, it often has oversights that aren't spotted until you've built them.

[onion2k]

You still work in sprints and deliver features to the user regularly, and iterate to the right solution. I'm not suggesting you design all the code in the entire app and write all the necessary tests for every feature at the beginning; you still only design the bits that are needed right now. The development process just has a lot more upfront thought time, more upfront test writing time, and less coding time because if your code passes the tests you know it's correct (based on the assumptions about what 'correct' is right now.) There's always going to be a requirement to go back and improve things, pay down technical debt, fix design issues, etc no matter what your development approach is.