testing-concept-outside-in-testing caused him to develop the interface he wanted on the ActiveRecord model (which was just stubbed up until this episode). Now that he has implemented the ActiveRecord model, its interface is entirely custom and easily consumable. None of the standard ActiveRecord methods like create! are used.
At 26:40 "I've been toying with this hypothesis that fast tests lead to good code. It might be a bi-directional relationship. If the tests have to be slow, it might be because there are issues in the code. If the tests are fast, it might be because the code is well factored. (other guy) A lot of times, if your tests are slow it's because you have a lot of coupling between your classes, so they're difficult to test in isolation, so you involve all these other parts, and that makes it slow."
Those non-DRY tests from 0052 kinda came back to bite him a little bit, but he was able to solve the problem readily with a vim macro.