Hello everybody,
I’m following along the Programming Phoenix 1.4 Book.
And at a moment we have the following simple code that do an HTTP request using erlang :httpc (excerpt simplified):

defp fetch_data(url) do
  {:ok, res} = :httpc.request(url)
  res
end

And for testing purpose, we want to mock the HTTP request from :httpc.
But for that we defined in the regular code itself a “conditional” use of the mock instead of the regular library when the code is running in the tests.
So we first defined a config option for the test environment in config.test.exs like so:

# config/test.exs
config :info_sys, :wolfram, http_client: InfoSys.Test.HTTPClient

That it triggers the mock HTTPClient in the module InfoSys.Test.HTTPClient when running in the test environment thanks to the following code in the code (located in a module named Wolfram in the example):

# lib/info_sys/wolfram.ex
@http Application.get_env(:info_sys, :wolfram)[:http_client] || :httpc
defp fetch_data(url) do
  {:ok, res} = @http.request(url)
  res
end

So we’re using :httpc in all environment but the test environment.

Now the mock HTTP client is in an Elixir Script file located somewhere within the test directory:

# test/backends/http_client.exs
defmodule InfoSys.Test.HTTPClient do
  def request(url)
    ...
    data
  end
end

In order to this to work we carefully included the code to be required in top of the test_helper.exs file:

# test/test_helper.exs
Code.require_file("backends/http_client.exs", __DIR__)
ExUnit.start()

Now everything work but I always get the following warning:

warning: InfoSys.Test.HTTPClient.request/1 is undefined (module InfoSys.Test.HTTPClient is not available or is yet to be defined)
  lib/info_sys/wolfram.ex:4 InfoSys.Wolfram.fetch_data/1

Here I put back the code where the warning is located:

# lib/info_sys/wolfram.ex
@http Application.get_env(:info_sys, :wolfram)[:http_client] || :httpc
defp fetch_data(url) do
  {:ok, res} = @http.request(url) # Warning on this line
  res
end

This warning really bothers me and I didn’t find a way to get rid of the warning.
I guess that this is related to the lack of .beam file generated for .exs files.
So I even tried to change the mock module inside a .ex file, but it seems that since it’s in the test folder it didn’t get compiled and that I still to use the Code.require_file to make it work.

Has anyone have any idea on how to clean up this warning?

Thank you very much.