Testing controller concerns in Rails

authentication_spec.rb

# This is an example spec that uses the ControllerConcernHelper module
require "rails_helper"

describe Authentication, type: :controller_concern do
  controller do
    include AbstractController::Callbacks

    before_action :authenticate

    def test_action
      render text: authenticated_device.id
    end
  end

  context "when no authentication is supplied" do
    it "responds with 401 Unauthorized" do
      expect(request.get("/").status).to eq 401
    end
  end

  context "when correct authentication is supplied" do
    let!(:secret) { SecureRandom.uuid }
    let!(:device) { create(:device, secret: secret) }
    let!(:response) { request.get("/", authenticate(device.id, secret)) }

    it "responds with 200 OK" do
      expect(response.status).to eq 200
    end

    it "finds device ID" do
      expect(response.body.chomp).to eq device.id
    end
  end

  context "when incorrect authentication is supplied" do
    it "responds with 401 Unauthorized" do
      authentication = authenticate(SecureRandom.uuid, SecureRandom.uuid)
      response = request.get("/", authentication)
      expect(response.status).to eq 401
    end
  end
end

controller_concern.rb

module ControllerConcernHelper
  module ClassMethods
    def controller(&block)
      before { controller(&block) }
    end
  end

  def controller(&block)
    @controller ||= begin
      concern = described_class
      Class.new(ActionController::Metal) do
        include concern
      end
    end
    @controller.class_eval(&block) if block
    @controller
  end

  def app
    @controller.action(:test_action)
  end

  def request
    Rack::MockRequest.new(app)
  end
end

RSpec.configure do |config|
  config.include ControllerConcernHelper, type: :controller_concern
  config.extend ControllerConcernHelper::ClassMethods, type: :controller_concern
end