I've been working on some slightly complicated code with a myriad of bad design decisions over the course of a decade, and a total absence of test suite. I knew I needed some code reusability in my tests but I had no idea of exactly how much without making a quick start. Meanwhile my brain was filled with ancient code from which I was expurgating zombies, and had issues understanding multi-vendor interactions, so I wanted some bare minimum reusability to make engineering failure conditions easier.