Testing Rack::Date with RSpec and Rack::MockRequest

rack_date.rb

require "rack"

class Rack::Date
  def initialize(app)
    @app = app
  end

  def call(env)
    status, headers, body = @app.call(env)
    headers.merge! 'Date' => Time.now.httpdate
    [status, headers, body]
  end
end

rack_date_spec.rb

require "./rack_date.rb"
require "rspec"

describe Rack::Date do
  let(:app) { proc{[200,{},['Hello, world.']]} }
  let(:stack) { Rack::Date.new(app) }
  let(:request) { Rack::MockRequest.new(stack) }

  let(:time) { Time.parse('November 19, 2013 11:30:24') }
  before { Time.stub(:now).and_return(time) }

  describe 'Date header' do
    let(:response) { request.get('/') }
    it { expect(response.headers['Date']).to eq time.httpdate }
  end
end