how to require my library in chef ruby_block

I'm developing a cookbook to deploy a simple ROR application. I write an app_helper.rb and put it into the libraries directory of my cookbook, here is the content:

module AppHelper

    def self.find_gem
      if File.exists?("/usr/local/rvm/bin/rvm")
        return `/usr/local/rvm/bin/rvm default exec which gem`.chomp
      else
        return "/usr/bin/gem"
      end
    end
  end

In the recipes/default.rb, I mix in the above module into Chef::Recipe class

class Chef::Recipe
  include AppHelper
end

As you know, the find_gem function can be called from anywhere of the recipe.

when I'm trying to use the find_gem function in my ruby_block like this:

ruby_block "find gem" do
   block do
    gem_bin = Chef::Recipe::find_gem
    # or gem_bin = find_gem
  end
end

I got a NoMethodError: undefined method 'find_gem'.

Also try to mix in the module into Chef::Resource::RubyBlock, it doesn't work neither.

class Chef::Resource::RubyBlock
  include AppHelper
end

ruby_block "find gem" do
   block do
    gem_bin = Chef::Resource::RubyBlock::find_gem
    # or gem_bin = find_gem
  end
end

Is there any way to call the function in the module from the ruby_block? Or Is there an variable of chef to location the files in the libraries, so that I can be able to require the module in the ruby_block.

Thanks!