How to do integration tests without controllers?

I've done integration (aka "feature") tests with rspec and capybara, but I'm building a complex piece of functionality that combines various ruby classes and rails models and there is no controller or UI involved really.

I'd like to perform a series of tests that touches these various classes and models to make sure they all work together as expected.

This doesn't seem like a unit testing as these tests require that multiple objects work together.

It also doesn't seem like traditional rails "integration" tests, since I'm not navigating a UI or hitting controllers.

So what are these and how can I build and organize them in my rails app?