Accessing app errors when using Capybara/Selenium with RSpec

exception_helper.rb

# -*- encoding : utf-8 -*-
# Because Capybara.app gets run by Thin in a separate thread, errors raised in
# the application during request_specs get hidden and just show up in the
# selenium-controller browser as 500 errors with no extra info. This module
# helps us dig into those errors.
module RequestSpecs
  module ExceptionHelper

    @@last_exception = nil

    def self.last_exception
      @@last_exception
    end

    def self.last_exception=(e)
      @@last_exception = e
    end

    class Middleware

      def initialize(app)
        @app = app
      end

      def call(env)
        begin
          @app.call(env)
        rescue Exception => e
          ExceptionHelper.last_exception = e
          Rack::Response.new('error in app', 500).finish
        end
      end
    end
  end
end

RSpec.configure do |config|

  config.before(:each, type: :request) do
    Capybara.app = RequestSpecs::ExceptionHelper::Middleware.new(Capybara.app)
  end

  config.around(:each, type: :request) do |example|
    example.run
    app_exception = RequestSpecs::ExceptionHelper.last_exception
    if !example.metadata[:allow_errors] && app_exception
      RequestSpecs::ExceptionHelper.last_exception = nil
      @example.instance_variable_set(:@exception, app_exception)
    end
  end
end