When testing the code of page 118 in iex -S mix i think you should get:
iex(1)> Mastery.Boundary.QuizValidator.errors(%{mastery: 3})
[title: "is required"]
But instead you get:
iex(1)> Mastery.Boundary.QuizValidator.errors(%{mastery: 3})
:ok
This could be fixed by changing the first line of Page 118 (lib\mastery\boundary\validator.ex) from
defp check_field(:ok, _errors, _field_name), do: :ok
to
defp check_field(:ok, errors, _field_name), do: errors
Is this right?