`mix test` should skip no test case apps in umbrella project

[cpunion]

In an umbrella project, when I execute mix test, it outputs errors and abort:

** (Mix) Cannot run tests because test helper file "test/test_helper.exs" does not exist

Since some apps no test folder.

I think mix test should skip these apps becase they are linked from external repository.

[josevalim]

@cpunion Can you tell us a bit more about your project? Why don't you have those external repositories as dependencies instead? Do you still want to compile them, even though you don't want to run their tests?

[cpunion]

Because this project structure and modules wrote by others for several years, I want to write some test cases with elixir, and don't make a big change, I am not the project owner. I just want to add a mix.exs file and test folder, so others will like and accept elixir. Seems mix is not fullly compatible with rebar? Or should I choose rebar_elixir_plugin?

[josevalim]

Ah, I see. We can provide an option that allows you to choose which apps to be part of a mix umbrella project. This is what we discussed anyway for #1730. That would work, right?

[cpunion]

Seems good, I'm waiting for it. Thanks.