Rack Middleware Test example (tweaked to work for me)

gistfile1.rb

class SampleMiddleware
  def initialize(app)
    @app = app
  end

  def call(env)
    request = Rack::Request.new(env)
    request.session['hello'] = 'world'
    @app.call(env)
  end
end

describe SampleMiddleware do
  include Rack::Test::Methods

  let(:inner_app) do
      lambda { |env| [200, {'Content-Type' => 'text/plain'}, ['All good!']] }
  end

  let(:app) { SampleMiddleware.new(inner_app) }

  it "adds hello:world to session" do
      get "/"
      last_request.session['hello'].should == 'world'
  end

  it "makes no change to response status" do
      get "/"
      last_response.should be_ok
  end
end