Exercises from "Programming Elixir >= 1.6" by Dave Thomas (not the KFC guy)
$ mix test
$ mix test test/example_test.exs
place require IEx; IEx.pry
wherever you'd like to pause execution
$ iex -S mix test test/example_test.exs
$ mix test.watch test/example_test.exs
$ mix run benchmarks/example_benchmark.exs