How can I test logger-messages with MiniTest?

I have an application and I want to test if I get correct messages from my logger.

A short example (you may switch between log4r and logger):

gem 'minitest'
require 'minitest/autorun'
require 'log4r'
#~ require 'logger'
class Testlog < MiniTest::Test
  def setup
    if defined? Log4r
      @log = Log4r::Logger.new('log')
      @log.outputters << Log4r::StdoutOutputter.new('stdout', :level => Log4r::INFO)
    else
      @log = Logger.new(STDOUT)
      @log.level = Logger::INFO
    end
  end

  def test_silent
    assert_silent{ @log.debug("hello world") }
    assert_output(nil,nil){ @log.debug("Hello World") }
  end
  def test_output
    #~ refute_silent{ @log.INFO("Hello") }#-> NoMethodError: undefined method `refute_silent'        
    assert_output("INFO log: Hello World\n",''){ @log.info("Hello World") }
  end

end

But I get:

  1) Failure:
Testlog#test_output [minitest_log4r.rb:27]:
In stdout.
Expected: "INFO log: Hello World\n"
  Actual: ""

On my output screen I see the message. I have similar results with Log4r::StderrOutputter and Log4r::Outputter.stdout.

So it seems it is send to the output screen, but it is not catched by minitest in STDOUT or STDERR.

Before I start to write a minitest-log4r-Gem:

Is there a possibility to test logger-output in minitest?

---

If not: Any recommendations how to implement a minitest-log4r-Gem?

Examples what I could imagine:

• define new outputter for minitest (Log4r::MinitestOutputter)
• Mock the logger.
• new assertions (add the new outputter as parameter?):
  • assert_message('INFO log: Hello World'){ @log.info("Hello World") }
  • assert_messages(:info => 1, :debug => 2){ @log.info("Hello World") } to count messages.
  • assert_info_messages('Hello World'){ @log.info("Hello World") }
  • assert_debug_messages('Hello World'){ @log.info("Hello World") }

In meantime I created a minitest-logger-Gem

A code example how to use it:

require 'log4r'
require 'minitest-logger'

class Test_log4r < MiniTest::Test
  def setup 
    @log = Log4r::Logger.new('log')
    @log.level = Log4r::INFO
  end    
  def test_output_1 
    assert_log(" INFO log: Hello World\n"){ @log.info("Hello World") }
  end
  def test_output_regex
    assert_log(/Hello World/){ @log.info("Hello World") }
  end  

  def test_silent
    assert_silent_log(){
      @log.debug("Hello World")
      #~ @log.info("Hello World")     #uncomment this to see a failure
    }
    refute_silent_log(){
      @log.warn("Hello World")     #comment this to see a failure
    }
  end

end

During the test a temporary outputter is added to the logger @log. After the test the outputter is removed again.

The gem supports log4r and logger.