I’m trying to mock ExTwitter during tests, I’m using https://github.com/plataformatec/mox for that.

In my code I use a config variable to do the Dependency Injection, like this:

config :my_app,
  # DI
  twitter_client: MyApp.TwitterClient

I’ve defined my mock in test/support/mocks.ex as per Mox docs like this

Mox.defmock(MyApp.Mocks.TwitterClient, for: MyApp.TwitterClient)

and in my test.exs config I have

config :my_app,
  # DI
  twitter_client: MyApp.Mocks.TwitterClient

Everything worked while incrementally compiling during development, however on a fresh checkout without any _build folder i get this error:

== Compilation error in file test/support/mocks.ex ==
** (ArgumentError) module MyApp.TwitterClient is not available, please pass an existing module to :for
    lib/mox.ex:92: Mox.validate_behaviour!/1
    lib/mox.ex:84: Mox.defmock/2
    (elixir) lib/kernel/parallel_compiler.ex:121: anonymous fn/4 in Kernel.ParallelCompiler.spawn_compilers/1

if I remove that mock line, compile and add the line back everything works. It seems like it’s trying to compile the mock file first and then the lib folder.

My elixirc_paths is ["lib", "test/support", "test/factories"] so lib comes first, any idea?

I’ve pushed a sample app with the problem in https://github.com/alex88/myapp just run mix test