Since Elixir 1.5 the recommened approach for starting processes in a test is to use start_supervised/2. This is an easy way to ensure the process is started and stopped together with the test process.

What I typically do for this situation is set something like this in config/test.exs:

config :my_app, :env, :test

Then in my application supervisor, I separate out the processes I don’t want to start automatically and check the env.

children = [{MyApp.Endpoint, []), {MyApp.Repo, []}]

children = case Application.get_env(:my_app, :env) do
  :test -> children ++ [{MyApp.OtherThing, []}]
  _ -> children
end

Supervisor.init(children, strategy: :one_for_one)

If there’s a better way than this, I’m not aware of it.

It seems that the easiest way to solve it is just to start your GenServer under a different name, using the :name option? Though if your GenServer functions depend on a hardcoded :name such as __MODULE__ it would indeed making testing harder.

e.g. instead of writing

  def start_link(_) do
    GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
  end

write

  def start_link(opts) do
    GenServer.start_link(__MODULE__, :ok, opts)
  end

and then the child spec:

      %{
        id: MyApp.MyGenServer,
        start: {MyApp.MyGenserver, :start_link, [[name: MyApp.MyGenServer]]}
      }

then in your test you can give a different name, e.g.

  setup context do
    _ = start_supervised!({MyApp.MyGenserver, name: context.test})
    %{producer: context.test}
  end

You just need to tear it down after, see another thread already talking about this at:

The setup callback needs you to return one of those types. Like:

setup do
  start_supervised(CeresCore.Queue.Consumers.PaymentConsumer)
  :ok
end

The other issue appears to be that CeresCore.Queue.Consumers.PaymentConsumer.start_link/1 is not a function that exists.