Steve Klabnik wrote a great article called Rails has Two Default Stacks. This is the best mental model I’ve found for the major factions within the rails community.
It breaks down if you start considering various deployment options, but I realized that it’s better not to. Deployment stacks can change more rapidly, and have more reasons for needing to change, than development stacks. It is worth just thinking about the development stack, of which testing is a major part. It is the development stack that plays the biggest role in programmer happiness.
If you work on a large project, thinking about just the development side of things will probably make your (Dev)Ops people happy, too.