In the "What Goes in Active Records" series (part 1 and part 2), we looked at some design constraints for what goes in ActiveRecord models. Sometimes, these constraints can lead to very small classes being extracted, which often feels awkward.
This screencast looks at one such class: a single line of service code with an alarmingly long test file. By creating a new value class and tightening the service's interface around it, we shorten the tests slightly. Then, by collapsing the service into the new value class, we shorten them even more. We're left with tests that are easier to reason about, and with a new abstraction reified in the code.
Finally, although this isn't stated in the screencast, the tests are fully isolated from Rails after this refactoring, whereas the original tests integrated with it. The new tests are about eight times faster (and will remain fast even as the application grows).