matchers.rb

require 'rspec/expectations'

RSpec::Matchers.define :be_a_created_for do | expected |
  match do | actual |
    expect(actual).to have_http_status(:created)
    expect(actual.headers["Location"]).to eql("http://test.host/websites/2")
  end
  failure_message do |actual|
"Expected response to be a <created>, but was #{actual.status}
Expected Location to be a <was this?>, but was #{actual.headers['Location']}"
  end
end

website_controller_spec.rb

  describe "POST create" do
    describe "with valid params" do
      it "creates a new Website" do
        expect {
          post :create, {:website => valid_attributes}, valid_session
        }.to change(Website, :count).by(1)
      end

      it "assigns a newly created website as @website" do
        post :create, {:website => valid_attributes}, valid_session
        expect(assigns(:website)).to be_a(Website)
        expect(assigns(:website)).to be_persisted
      end

      it "redirects to the created website" do
        post :create, {:website => valid_attributes}, valid_session
        expect(response).to be_a_created_for(Website.last) 
      end
    end

    describe "with invalid params" do
      it "assigns a newly created but unsaved website as @website" do
        post :create, {:website => invalid_attributes}, valid_session
        expect(assigns(:website)).to be_a_new(Website)
      end

      it "re-renders the 'new' template" do
        post :create, {:website => invalid_attributes}, valid_session
        expect(response).to render_template("new")
      end
    end
  end