Testing a class method

movie.rb

class Movie < ActiveRecord::Base
  def self.all_ratings
    # debugger
    find_by_sql("SELECT DISTINCT rating FROM movies").map(&:rating)
  end
end

movie_test.rb

require 'minitest/autorun'
require 'ostruct'
require 'debugger'
require_relative '../minitest_helper_lite'
stub_module 'ActiveRecord::Base'
require_relative '../../app/models/movie'

describe Movie do
  before do
    @it = Movie.new
  end

  describe "#all_ratings" do
    it "returns all unique MPAA movie ratings" do
      stub(@it).rating { '' }
      stub(Movie).find_by_sql("SELECT DISTINCT rating FROM movies") do
        ['G', 'PG-13', 'R', 'R', 'G', 'PG'].map! do |r|
          stub(Movie.new).rating { r }
        end
      end 

      ['G', 'PG-13', 'R', 'PG'].each do |rating|
         Movie.all_ratings.must_include rating
      end
    end
  end
end