Rails compatible method logging. Use this to log all calls to instance methods of a class to the log.

method_logger_test.rb

# converted to stand-alone script

require 'minitest/autorun'
require 'minitest/unit'
require 'stringio'

# fake out the logger
class Rails
  @@logger = StringIO.new

  def self.logger
    @@logger
  end
end

module MethodLogger
  def self.included(base)
    methods = base.instance_methods(false) + base.private_instance_methods(false)
    base.class_eval do
      methods.each do |method_name|
        original_method = instance_method(method_name)
        define_method(method_name) do |*args, &block|
          Rails.logger.puts "-> #{base}##{method_name}(#{args.inspect})"
          return_value = original_method.bind(self).call(*args, &block)
          Rails.logger.puts "<- #{base}##{method_name} #=> #{return_value.inspect}"
          return_value
        end
      end
    end
  end
end

class Model
  def foo
    "bar"
  end

  # maybe inside Rails, things are different enough to allow including the module at 
  # the top of the class, but in stand-alone the include must come after the methods
  # have been defined for this to work.
  include MethodLogger
end

class TestMethodLogger < MiniTest::Unit::TestCase
  def test_it
    model = Model.new
    model.foo
    Rails.logger.rewind
    assert_equal "-> Model#foo([])\n<- Model#foo #=> \"bar\"\n", Rails.logger.read
  end
end