Rail’s engines can be a bit of a pain to write tests for. Since they don’t run in the full Rails stack it requires a bit of pain to setup anything but the most basic testing. test_engine solves this problem by making it almost as easy to write tests in your engine as it is to write tests in your Rails app. If you have been holding out on testing your engines because you don’t know a good way to implement it maybe this is your ticket to get back on track.