Hide external access behind a small facade for easy mocking

Imagine you have validation like this, where you call the youtube website to make sure the provided video id is valid:

    1 class Video < ActiveRecord::Base
    2   def validate
    3     response = Net::HTTP.start('youtube.com') { |http| http.head("/v/#{self.youtube_video_id}") }
    4     unless response.is_a?(Net::HTTPOK)
    5       errors.add(:youtube_video_id, "no valid Youtube Video ID")
    6     end
    7   end
    8 end
    9 

Actually, this code fragment is a pain in the neck to test. If you hide the external access behind a small facade (or wrapper if you like) like this:

    1 class YouTube
    2   def self.video_id_valid?(video_id)
    3     response = Net::HTTP.start('youtube.com') do |http|
    4       http.head("/v/#{self.youtube_video_id}")
    5     end
    6     response.is_a?(:Net::HTTPOK)
    7   end
    8 end
    9
   10 class Video < ActiveRecord::Base
   11   def validate
   12     unless Youtube.video_id_valid?(self.youtube_video_id)
   13       errors.add(:youtube_video_id, "no valid Youtube Video ID")
   14     end
   15   end
   16 end
   17 

it's much easier to test:

    1 # video_spec.rb
    2 describe Video, "validations" do
    3   before(:each) do
    4     @video = Video.new(:youtube_video_id => 'iY6VroKoB8E')
    5   end
    6   it "should succeed with correct youtube video id" do
    7     Youtube.stub!(:video_id_valid?).and_return(true)
    8     @video.should be_valid
    9   end
   10   it "should fail with incorrect youtube video id" do
   11     Youtube.stub!(:video_id_valid?).and_return(false)
   12     @video.should_not be_valid
   13   end
   14 end
   15