How else do you know you're done? 

 But, do you ever feel stupid writing the code for the first green?   Like, how do you keep from mentally pre-refactoring everything and ending up with bloated code that does more than turn the test green?

I just started doing this, and it's working, but it feels sorta silly. Like... this is actually kinda cool... but, this is it? 🤣  

 I always feel stupid writing code. 

 I've done some SAS, and it's just math->plot.
The test was just feeding it information and looking if the plot was reasonable. 😅 

I've done a lot of DB and test development, so this is a novel "mental frame" for me, programming a client that a human would interact with, directly. Good practice, tho.