I’m going to say it just is misinformation, if that’s what “lib” is here.

If I actually did have that kind of job, the tests-first philosophy would sound very appealing. Actually, build the stack so you don’t have a choice - the real code should just be an instantiation of plumbing on generic variables with certain expected statistical properties. You can do that when correctly processing unpredictable but repetitive stuff is the name of the game, and I expect someone does.

Depending on what kind of coding you’re doing, there might not be an obvious, really atomic unit to test. Most people here seem to do the data-plumbing-for-corporations kind, though.