On: Write tests. Not too many. Mostly integration

[maxxxxx]

To a certain degree you can unit test GUIs with tools like Ranorex or Selenium. The question is how much setup you need to get the GUI on the screen with the right data.

[pault → maxxxxx]

That isn't unit testing though, it's integration or e2e testing.

[pjmlp → maxxxxx]

You can, but usually with lots of effort and cannot test UX and design requirements anyway, which is why I tend to make this question about full TDD based processes.