Testing exceptions with Rack. Couldn't get it to work in conjunction with :driver => :selenium level tests, but it runs fine when run individually. Not 100% sure the tests are necessary given the tests around routes/controllers.

errors_request_spec.rb

require 'request_spec_helper'

describe "Errors" do
  context "test", driver: :rack_test do
    include Rack::Test::Methods

    def app
      app = Rack::Builder.new do 
        run Rewarder::Application
      end.to_app

      # We need these specifically for these tests, but I do not think that they 
      # are being applied correctly.
      app.config.consider_all_requests_local = false
      app.config.action_dispatch.show_exceptions = true

      app 
    end

    describe "for an invalid path error" do
      describe "for text/html requests" do
        before do
          get '/invalid/path'
        end

        it "shows the not_found page to the user" do
          expect(last_response.status).to eq(404)
          expect(last_response.body).to match /Oops! There are no Rewards to be found here\./m
        end
      end

      describe "for */* requests" do
        before do
          header('Accept', '*/*')
          get '/invalid_image.png'
        end

        it "show an empty page to the user" do
          expect(last_response.status).to eq(404)
          expect(last_response.body.strip).to be_empty
        end
      end
    end

    describe "when an error occurs within ErrorsController" do
      before do
        ApplicationController.any_instance.stub(:set_cache_header).and_raise(StandardError.new('An error occured...'))
        get '/'
      end

      it "shows the user our fall back error page" do
        expect(last_response.status).to eq(500)
        expect(last_response.body).to match /We're sorry, but something went terribly wrong/m
      end
    end

    describe "for a conflict error" do
      it "shows the internal_server_error page to the user"
    end

    describe "for an unprocessable entity error" do
      it "shows the internal_server_error page to the user"
    end

    describe "for an internal server error" do
      it "shows the internal_server_error page to the user"
    end
  end
end