Designing Elixir Systems With OTP

Test Your Boundary

This chapter has gone quickly. We built an integration test to work through the base mastery.exs API. We built only a single test, but it covered an end-to-end scenario with persistence enabled and a quiz. We even built in enough wrong and right answers to show that our mastery feature was working.

Next, we dove into specific persistence tests. We wrote tests to call our basic persistence function two different ways. Then we simulated an exception and followed that up with a brief test of our reporting function.

Along the way we experienced the impacts of the layering strategy we’ve used throughout this book. In particular, for each API we were able to isolate the concerns of our test to one sliver of complexity. After all, ...