Proposal: [ExUnit] with_application_env(key, value, update_fun, fun)

[Michael Schaefermeyer]

Hey all,

I regularly find myself changing the Application configuration in tests to temporarily adjust a setting (i.e. when using Bypass and changing the configured endpoint for HTTP requests).

My current workflow looks as follows:

test "something" do
  old_env = Application.get_env(:app, Module)
  new_env = Keyword.put(old_env, :key, value)
 
  Application.put_env(:app, Module, new_env)
 
  # Do something that reads the config
  Application.put_env(:app, Module, old_env)
end

Besides being quite repetitive it disallows async tests, as another test might be reading from the Application environment while this test is running.

Ideally, ExUnit would allow me to temporarily change the Application environment in a async-safe way:

test "something" do
  with_application_env :app, Module, fn(config) -> Keyword.put(config, :key, value), fn ->
    # Do something that reads the config
  end
end

Of course I could make the configuration module configurable and use something other than Application. The reason I am still suggesting this is that I feel like configuring your app via Application is still the way to go and I wouldn't want to diverge from that standard just for tests.

Hope that makes sense. I would love to hear your thoughts.

Thanks,
Michael

[Louis Pilfold]

Hi Michael

I've written a tiny lib for this -> https://github.com/lpil/temporary-env

Perhaps you might find this useful :)

Cheers,
Louis

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[Michael Schaefermeyer]

It definitely is, thanks Louis!

Figuring that this is something other people might need as well I wondered if it was worthwhile to put it ExUnit directly (and make it work with async).

[Louis Pilfold]

Hey

Mix config is global mutable state, so I'm not sure how you could handle this asynchronously.

Personally I prefer to avoid mix config where possible an instead pass values down through the supervision tree. :)

Cheers,
Louis

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