recipe compile error

rest_client.rb

# sock::default recipe
chef_gem 'rest-client'

# libraries/sock.rb
class Chef::Recipe::Sock
  require 'rest_client'
  
  #.....
end

# error

#     Compiling Cookbooks...
#
#       ================================================================================
#       Recipe Compile Error in /tmp/kitchen/cache/cookbooks/sock/libraries/sock.rb
#       ================================================================================
#
#       LoadError
#       ---------
#       cannot load such file -- rest_client
#
#       Cookbook Trace:
#       ---------------
#         /tmp/kitchen/cache/cookbooks/sock/libraries/sock.rb:2:in `<class:Sock>'
#         /tmp/kitchen/cache/cookbooks/sock/libraries/sock.rb:1:in `<top (required)>'
#
#       Relevant File Content:
#       ----------------------
#       /tmp/kitchen/cache/cookbooks/sock/libraries/sock.rb:
#
#         1:  class Chef::Recipe::Sock
#         2>>   require 'rest_client'
#         3:    attr_accessor :user, :node, :url
#         4:    attr_writer :password
#         5:
#