Sometimes you want to test all those private functions in your modules. But Elixir doesn't make it easy to get to them. As a result, you end up trying to exercise them by setting up convoluted calls to the public API.

private to the rescue. It switches the visibility of functions so that they are exposed when the Mix environment is :test, and private otherwise.

defmodule MyMod do
  use Private

  def api1() do ...
  def api2() do ...

  private do
    def helper1() do...
    def helper2() do...
  end

  def api3() do ...

  private do
    defp helper3() do...
  end
end

All functions in the private block will be defined as private unless the Mix environment is :test.

In the test environment, def will be left unchanged, and defp will be changed to def. In all other environments, def will be changed to defp and defp will be left unchanged.

@deps [
  { private: "> 0.0.0" ],
]