method_logging.rb

module MethodLogging
  def self.logger=(logger)
    @@logger = logger
  end

  def self.included(base)
    base.extend(ClassMethods)
  end

  def log(method, something)
    @@logger.debug("Calling %s#%s with %s" % [method.owner, method.name, something])
  end

  module ClassMethods

    def log_method(*methods)
      @logged_methods    ||= Set.new
      @annotated_methods ||= Set.new
      @logged_methods += methods
      ((instance_methods.to_set & @logged_methods) - @annotated_methods).each { |m| add_logging(m) }
    end

    def add_logging(method)
      return if @annotated_methods.include?(method)
      @annotated_methods << method
      old_method = instance_method(method)

      define_method(method) do |*args|
        log(old_method, args)
        old_method.bind(self).call(*args)
      end
    end

    def method_added(method)
      return unless @logged_methods.include?(method)
      return if @working_on == method

      @working_on = method
      @annotated_methods.delete(method)
      (@logged_methods & [method]).each { |m| add_logging(m) }
      @working_on = nil
    end
  end
end

class Example
  include MethodLogging

  log_method :echo

  def echo(message1, message2)
  end
end

describe "" do
  it "" do
    logger = spy('logger')
    MethodLogging.logger = logger
    x = Example.new
    x.echo("Hello", "world")

    expect(logger).to have_received(:debug).with("Calling Example#echo with [\"Hello\", \"world\"]")
  end
end