For your vector issue, I’d go the route of some static examples if possible. Do you have a way to manually work out the answer that your code is trying to achieve?

Not necessarily. In this scenario I'd imagine it's a series of numbers as opposed to something more human-friendly exactly because there's internal complexity that's important but hard to manually survey, let alone generate. If you've worked with GANs at all, maybe it's a point in a latent space.

For side effects, that may indicate what I referred to as tightly coupled code. Could you give an example of what you mean by “side effect”?

I mean it in the standard functional language way, if you're familiar. There's an operation that happens at some step of an algorithm, and it changes a data structure which is referred to or updated at another step. Sometimes you can't really avoid it, because the problem itself has an interconnection like that.