Yea what I've been trying to get across in this thread but apparently failing to do so is that it's a waste of time to write tests for a POC (unless you have like, a wrapper around a low level HTTP client that you have say, a GET and POST method, there's nothing wrong with writing simple tests for that since that's not going to change) until after you've gone through enough review iterations to confirm with all involved that everything looks good. If something comes up after that, I think it's a scope change and an entirely different can of worms.
For personal projects I feel like a hard spec outside of a braindump of what you want to do really hinders you even more. Unless you have a good deal of experience in the domain you're working in I feel like you end up "prematurely optimizing" your API ergonomics because you've written out a bunch of API endpoint/method definitions without letting a workflow emerge.
Long story short, make it work, make it clean, make it fast.
Three thousand years of beautiful tradition, from Moses to Sandy Koufax, you're god damn right I'm living in the fucking past