Warning when configuring :mix_test_watch in Umbrella project

[smt116]

This is exactly the same issue as described in #28. However, moving the options under the dev configuration (via if statement or using dedicated config/dev.exs file) does not solve the problem when the package is added to the root mix.exs of the umbrella project.

Steps to reproduce

1. Run mix new sample_umbrella --umbrella,

2. Run cd sample_umbrella,

3. Apply the following changes:

   diff --git a/config/config.exs b/config/config.exs
   index ab23e80..6690b3f 100644
   --- a/config/config.exs
   +++ b/config/config.exs
   @@ -16,3 +16,7 @@ import Config
    #       format: "$date $time [$level] $metadata$message\n",
    #       metadata: [:user_id]
    #
   +
   +if Mix.env == :dev do
   +  config :mix_test_watch, clear: true
   +end
   diff --git a/mix.exs b/mix.exs
   index 0d95de0..7dcb200 100644
   --- a/mix.exs
   +++ b/mix.exs
   @@ -16,6 +16,6 @@ defmodule SampleUmbrella.MixProject do
      #
      # Run "mix help deps" for examples and options.
      defp deps do
   -    []
   +    [{:mix_test_watch, "~> 1.0", only: :dev, runtime: false}]
      end
    end
   diff --git a/mix.lock b/mix.lock
   new file mode 100644
   index 0000000..3c731c5
   --- /dev/null
   +++ b/mix.lock
   @@ -0,0 +1,4 @@
   +%{
   +  "file_system": {:hex, :file_system, "0.2.10", "fb082005a9cd1711c05b5248710f8826b02d7d1784e7c3451f9c1231d4fc162d", [:mix], [], "hexpm", "41195edbfb562a593726eda3b3e8b103a309b733ad25f3d642ba49696bf715dc"},
   +  "mix_test_watch": {:hex, :mix_test_watch, "1.0.2", "34900184cbbbc6b6ed616ed3a8ea9b791f9fd2088419352a6d3200525637f785", [:mix], [{:file_system, "~> 0.2.1 or ~> 0.3", [hex: :file_system, repo: "hexpm", optional: false]}], "hexpm", "47ac558d8b06f684773972c6d04fcc15590abdb97aeb7666da19fcbfdc441a07"},
   +}

4. Start the console: iex -S mix

5. Notice the following output:

   Erlang/OTP 23 [erts-11.1.8] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe]

   You have configured application :mix_test_watch in your configuration file,
   but the application is not available.

   This usually means one of:

   1. You have not added the application as a dependency in a mix.exs file.

   2. You are configuring an application that does not really exist.

   Please ensure :mix_test_watch exists or remove the configuration.

   Interactive Elixir (1.11.3) - press Ctrl+C to exit (type h() ENTER for help)
   iex(1)>

Workaround

To suppress the warning, you need to add the dependency to one of the applications.