page_fetcher.rb

require 'net/http'

class PageFetcher
  def fetch(url)
    @response = Net::HTTP.get_response URI(url)
    Response.new @response
  end

  class Response
    def initialize(response)
      @response = response
    end

    def success?
      @response.code == '200'
    end
  end
end

describe PageFetcher do
  describe '#fetch(url)' do
    let(:response) { double('response', code: '200') }

    before do
      allow(Net::HTTP).to receive(:get_response)
        .and_return(response)
    end

    it 'is successful' do
      expect(PageFetcher.new.fetch('http://example.com')).to be_success
    end
  end
end