Patch GenServer :handle/2 - Idea / question?

[Matsa59]

Hello I have some GenServer that subscribe to Phoenix.PubSub channel to reduce code coupling

I feel like something is missing Patch (that is really nice btw).

My workflow is everytime a character is created, I broadcast a message that will be catch by some GenServers to do their shit (e.g. send welcome email, push discord msg, or log the event in a db or w.e)

I want to test this but because it's a PhoenixPubSub event, it's not easily testable. I end with the following test (that works great).

defmodule ForHonor.Feed.AdventureEventSubscriberTest do
  use Patch
  #...

  test "on character created", %{character: character} do
    patch_handle_info(AdventureEventSubscriber)

    msg = {:character_created, character}
    Phoenix.PubSub.broadcast(ForHonor.PubSub, "game:events", msg)

    assert_handle_info(AdventureEventSubscriber)

    # test if side effect was apply or w.e
  end


  defp patch_handle_info(module) do
    pid = self()

    patch(module, :handle_info, fn msg, state ->
      real(module).handle_info(msg, state)
      |> tap(fn _ -> send(pid, module) end)
    end)
  end

  defp assert_handle_info(module, timeout \\ :timer.seconds(5)) do
    receive do
      ^module -> assert true
    after
      timeout -> assert false
    end
  end
end

I don't have a global overview of patch, maybe I miss something. I would like to have your opinion on the previous code. If their is no other way to accomplish that, are you interested by a pull request ?

Thanks a lot ;)

[ihumanable]

I don't see anything obviously wrong with the listing above, but you could simplify the test by using the following pattern.

defmodule ForHonor.Feed.AdventureEventSubscriberTest do
  use Patch
  #...

  test "on character created", %{character: character} do
    spy(AdventureEventSubscriber)

    msg = {:character_created, character}
    Phoenix.PubSub.broadcast(ForHonor.PubSub, "game:events", msg)

    assert_called AdventureEventSubscriber.handle_info(_, _)

    # test if side effect was apply or w.e
  end
end

Depending on the version you were running on there was an issue pre v0.8.0 where patching GenServer would break Patch.