Occasional failures of test "can use info level"

[LeeroyDing]

Sometimes when running tests, the named test would fail while others don't.

The failure looks like:

   1) test can use info level (Logger.Backends.JSON.UDPTest)
      test/json_logger_udp_test.exs:42
      ** (exit) exited in: GenEvent.call(Logger, {Logger.Backends.JSON, :test}, {:configure, [level: :info]}, 5000)
          ** (EXIT) no process
      stacktrace:
        (elixir) lib/gen_event.ex:561: GenEvent.call/4
        test/json_logger_udp_test.exs:43