I usually start with an exploratory prototype and go back and forth between coding and sketching things out in my notebook. After it's clearer what the new fea

I usually start with an exploratory prototype and go back and forth between coding and sketching things out in my notebook. After it's clearer what the new feature is, I go back to the existing project's repo an start building it. I raid whatever code is useful from the prototype as I do so. In the case of a completely new project, I still start with a prototype and frequently discard and rewrite it after getting more clarity. I don't write any tests during the sketching/prototyping phase.