This is a pretty straightforward utility function that wouldn't be that hard to test. It's normal to have standards for code coverage as part of the review process, I don't code in C but I'd be surprised if setting any of that up is actually that burdensome.

I disagree with your reference of that quote being applicable here though. In fact, adding unit tests is the exact opposite: that quote is saying 'if your answer is "make less mistakes" ....' Unit tests in general are an acceptance of the fact that we will fail to be perfect and we need to mitigate that with extra checks. The article already said it had two human reviewers, so they're not opposed to extra process to help ensure quality, unit tests are just another (actually very cheap) extra step.