RoR doesn't "encourage" unit testing, it forces you to write thousands of meaningless unit tests which just make up for the lack of strong type system. Unit tests should test code logic, not parameter types.
Unit tests are meant to test behavior - When I do X, I want Y to happen.
Rspec is great for this - I did X, I should see A, B, and C get called - and if they return to me this value then my final result should be Z.
I've written several RoR apps in the past where I didn't unit test at all. Perhaps I misunderstood you.