> My concern with TDD is that writing tests necessarily implies designing an API upon which those tests operate

It really forces you to do outside-in testing; I usually describe the kind of API I want when chatting with the agents. For example, the CLI options, the routes that might be useful for an API, etc.

> I look at the code and find a rats nest / ball of mud that will cost 10x more tokens to enhance should I ever need to add a feature.

Agreed, I don't know if there are good forcing functions to avoid complexity. The providers have a huge incentive to have you waste your tokens (for example when it re-outputs the complete file when you ask for a tiny change).

In "proper" TDD you you supposed go:

- write a test for method that does not exist, it just calls the method and nothing else

- write method that does nothing

- add/extend test that uses that method <-- this very loop starts

- modify method until tests passes

- go back to loop start until you're done

I always hated it. When I work with LLM i first massage interface that tests, then tests, then implementation until all these tests pass.

> for example when it re-outputs the complete file when you ask for a tiny change).

well with sonnet 3.5 and 4.5 (can't say about 4.6) it often will get stuck in a loop trying to update just the required parts and iether waste tons of tokens doing these updates or waste tons of tokens to a point where restring file from git is required. Tokens get wasted regardless.

“Test Driven Design” is another way to frame it.