This is a problem I’ve come across now and then… in an app, I have a few directories containing .json files (e.g. for example requests or responses). I put these files into directories inside of test/support/ and then in my mix.exs I reference the test/support/ directory as follows:

    def project do
    [
      # ...
      elixirc_paths: elixirc_paths(Mix.env()),
      # ...
    ]
  end

  # Specifies which paths to compile per environment.
  defp elixirc_paths(:test), do: ["lib", "test/support"]
  defp elixirc_paths(_), do: ["lib"]

The problem revolves around the __DIR__ variable because it is resolved at compile time. I can include files in my setup fixtures doing something like this:

 # example setup inside `test/support/conn_case.ex`
  defp append_mutation(%{mutation: mutation} = context) do
    data =
      "#{__DIR__}/mutations/#{mutation}.json"  # <-- resolves to /full/path/to/test/support/mutations/something.json
      |> File.read!()
      |> Jason.decode!()

    %{context | mutation: data}
  end

When I run tests locally, the path gets converted to paths that make sense on my local machine, so tests pass. However, if I then try to run tests in a containerized environment (e.g. via docker-compose), the paths are not the same, so tests fail.

One option is to do mix compile --force before running the tests, but that’s slow – I have to recompile everything every time I switch environments.

I seem to remember something about the https://hexdocs.pm/elixir/Application.html#app_dir/1 working in certain cases here… but I don’t see how it’s working its magic. Even with my mix.exs set to compile my test/support/ folder, none of my supporting .json files end up in the _build/ folder, so I don’t think I can reference them there.

Can someone educate me on a better way to dealing with this?

Thanks!