I have a legacy Erlang app that is part of Mix umbrella project. The app has eunit tests that are ran using a custom Mix task. When migrating the whole project to Erlang/OTP 23 and Elixir 1.11 I switched logging from lager to Erlang logger (with Elixir backend) and for some reason logger config is not loaded from test.exs when running this custom eunit mix task - logger gets some default configuration with level: :all which is not ideal .

This is not really specific to this mix task, this is true for any mix task it seems. Maybe the logger app is started before the config is loaded?

For example:

defmodule Mix.Tasks.Hello do
  use Mix.Task
  require Logger

  def run(_) do
    IO.inspect(Application.get_all_env(:logger))
    # level is info:

    # [
    #   utc_log: false,
    #   translators: [{Logger.Translator, :translate}],
    #   backends: [:console],
    #   discard_threshold_for_error_logger: 500,
    #   handle_sasl_reports: false,
    #   truncate: 8096,
    #   discard_threshold: 500,
    #   compile_time_application: nil,
    #   sync_threshold: 20,
    #   discard_threshold_periodic_check: 30000,
    #   console: [level: :info, format: {LoggerFormatter, :format}, metadata: :all],
    #   handle_otp_reports: true,
    #   start_options: [],
    #   level: :info,
    #   translator_inspect_opts: [],
    #   compile_time_purge_matching: []
    # ]

    Logger.debug("!!!")
    # level is info in config but still a debug message is printed
    # !!!

    IO.inspect(:logger.get_config())
    # level: :all is set for Elixir handler

    # %{
    #   handlers: [
    #     %{
    #       config: %{ ... },
    #       filter_default: :stop,
    #       filters: [
    #         filter_non_ssl: {&:logger_filters.domain/2, {:log, :sub, [:otp, :ssl]}}
    #       ],
    #       formatter: {:ssl_logger, %{}},
    #       id: :ssl_handler,
    #       level: :debug,
    #       module: :logger_std_h
    #     },
    #     %{
    #       config: %{ ... },
    #       filter_default: :log,
    #       filters: [],
    #       formatter: {:logger_formatter, %{}},
    #       id: Logger,
    #       level: :all,
    #       module: Logger.Handler
    #     }
    #   ],
    #   module_levels: [ssl_logger: :debug],
    #   primary: %{
    #     filter_default: :log,
    #     filters: [process_disabled: {&Logger.Filter.process_disabled/2, []}],
    #     level: :debug
    #   },
    #   proxy: %{ ... }
    # }
  end
end

How and when is the Logger app started when Mix task is ran? Why is the specified env config not loaded?
Thanks!