debug an rails gem but pry didn't stop at the breakpoing

Question

I want to trace what does event_calendar do ,

So I added the gem then bundle install and I found its install location is at ~/.rvm/gems/ruby-1.9.3-p448/gems/event-calendar-2.3.3/generators/event_calendar

So I add require 'pry' and embedded the binding.pry in the line I want to debug,

However when I ran the rails g event_calendar

I thought it will invoke the event_calendar_generator.rb in ~/.rvm/gems/ruby-1.9.3-p448/gems/event-calendar-2.3.3/generators/event_calendar

However it didn't be blocked at the line I expected.

 1 require 'pry'
  2 require File.expand_path(File.dirname(__FILE__) + "/lib/insert_routes.rb")
  3 binding.pry
  4 class EventCalendarGenerator < Rails::Generator::Base
  5   default_options :static_only => false,
  6                   :use_jquery =>  false,
  7                   :use_all_day => false
  8
  9   attr_reader :class_name, :view_name
 10
 11   def initialize(args, runtime_options = {})
 12     super
 13     binding.pry
 14     usage if args.length > 0 and args.length < 2
 15     @class_name = (args.shift || "event").underscore
 16     @view_name = (args.shift || "calendar").underscore
 17   end