Suppress Logger when testing

Question

I wonder how to disable logging in Elixir when testing. In my current code I test for logger messages, so I don't want to disable it completely, but hide the messages until any test stop passing.

I'm using mix and ExUnit to manage and test my project.

mix test
Compiling 2 files (.ex)
.........
17:59:18.446 [warn]  Code seems to be empty
.
17:59:18.447 [warn]  Code doesn't contain HLT opcode
.
17:59:18.448 [warn]  Code doesn't contain HLT opcode

17:59:18.448 [error] Label error doesn't exist
.....

Finished in 0.07 seconds
16 tests, 0 failures

Answer 1

Either use ExUnit.CaptureLog:

import ExUnit.CaptureLog

test "example" do
   assert capture_log(fn ->
      Logger.error "log msg"
   end) =~ "log msg"
end

Or if you just want to ignore any logs then:

@tag capture_log: true
test "example" do
    Logger.error "log msg"
end

Answer 2

Into your config/test.exs file put the following config for the logger:

config :logger, level: :error

If you don’t have environment-specific configs, put the following line in your config/config.exs:

config :logger, level:
  case Mix.env do
    :test -> :error
    _ -> :info
  end

---

Another option would be to use another backend for the logging messages (assuming {:logger_file_backend, "~> 0.0"} is included in deps section of mix.exs):

config :logger,
  compile_time_purge_level: :debug,
  format: "$date $time $metadata[$level] $message\n",
  metadata: [:application, :module, :function, :file, :line],
  backends: [{LoggerFileBackend, :info_warn_error}]

config :logger, :info_warn_error,
  path: "log/info_warn_error.log", # or "/dev/null"
  level: :warn