Unable to use any_instance on Twitter gem's user_timline - ruby

Question

I am still quite fresh to Ruby, and especially testing in Ruby. Hopefully the code is not a trainwreck :) I am having issues using any_instance with the Twitter gem, while it works fine on my own classes.
This is (what I believe) the relevant code
require 'twitter'
require 'minitest/unit'
require 'mocha/mini_test'
omitting for brevity....
args = { id: 573536452149182464, id_str: 73536452149182464, text: 'This is an initial tweet from the user'}
initial_tweet = ::Twitter::Tweet.new(args)
::Twitter::REST::Timelines.any_instance.stubs(:user_timeline).returns(initial_tweet)
The code produces the following error:
Minitest::UnexpectedError: NoMethodError: undefined method `any_instance|' for Twitter::REST::Timelines:Module
Are principles to stubbing gems different, am I approaching it wrong?
EDIT: I have added the entire code for the two classes below.
twitter.rb
require 'rubygems'
require 'cinch'
require 'cinch/commands'
require 'twitter'
require 'shorturl'
module Gigabot
module Commands
class Twitter
include Cinch::Plugin
include Cinch::Commands
def initialize(bot)
super(bot)
#client = create_client
#follow = config[:follow]
#channels = bot.config.channels
#latest_tweets = Hash.new
set_initial_tweets
end
timer 60, method: :twitter_update
def twitter_update
#follow.each do |user|
new_tweet = #client.user_timeline(user, options = {exclude_replies: true}).first
if #latest_tweets[user] != new_tweet
short_url = ShortURL.shorten("https://twitter.com/#{user}/status/#{new_tweet.id}")
reply = Format(:bold, "<#{user}> ") + "#{new_tweet.full_text} [#{short_url}]"
reply = reply.gsub(/\n/,' ')
#channels.each {|channel| Channel(channel).send(reply)}
#latest_tweets[user] = new_tweet
end
end
end
private
def create_client
::Twitter::REST::Client.new do |c|
c.consumer_key = config[:consumer_key]
c.consumer_secret = config[:consumer_secret]
c.access_token = config[:access_token]
c.access_token_secret = config[:access_token_secret]
end
end
def set_initial_tweets
#follow.each do |user|
#latest_tweets[user] = #client.user_timeline(user, options = {exclude_replies: true}).first
end
end
end
end
end
twitter_test.rb
require 'twitter'
require 'minitest/unit'
require 'mocha/mini_test'
require File.dirname(__FILE__) + '/../../../helper'
require File.dirname(__FILE__) + '/../../../../lib/gigabot/commands/twitter'
module Gigabot
module Commands
class TwitterTest < TestCase
def setup
bot = Cinch::Bot.new
bot.loggers.level = :fatal
bot.config.plugins.options[Twitter] = {
consumer_key: 'test_key',
consumer_secret: 'test_key_secret',
access_token: 'test_access_token',
access_token_secret: 'test_access_token_secret',
follow: %w(follow1 follow2)
}
args = { id: 573536452149182464, id_str: 73536452149182464, text: 'This is an initial tweet from the user'}
initial_tweet = ::Twitter::Tweet.new(args)
::Twitter::REST::Timelines.any_instance.stubs(:user_timeline).returns(initial_tweet)
#plugin = Twitter.new(bot)
end
def test_create_twitter_client_on_initialize
refute_nil(#plugin.instance_variable_get(:#client))
end
end
end
end