Making Rails tests aware of Rack middleware outside Rails's internal chain

Question

Context: an application uses a piece of Rack middleware that must be setup in config.ru, rather than Rails's internal Middleware chain. This is for reasons not relevant to this question.

Question: how do I make my tests (functional and integration) aware of this middleware?

I'll ellaborate with an example. Let's create a pristine Rails 3 app, using rack-rewrite for illustration purposes.

# /config/initializers/example.rb
Rails.application.middleware.insert 0, 'Rack::Rewrite' do
 r301 '/so', 'http://stackoverflow.com'
end

# /test/integration/the_test.rb
require 'test_helper'

class TheTest < ActionDispatch::IntegrationTest
 test "redirect from /so to http://stackoverflow.com" do
   get '/so'
   assert_redirected_to 'http://stackoverflow.com'
 end
end

If you run the above test, all is good, and with the browser you can confirm that visiting the path /so will redirect you to StackOverflow indeed.

Cool, let's now set this up outside Rails then. Remove the file /config/initializers/example.rb described above, and change config.ru to the following:

# /config.ru
require ::File.expand_path('../config/environment',  __FILE__)

map '/so' do
  run Rack::Rewrite do
    r301 '', 'http://stackoverflow.com'
  end
end

map '/' do
  run Deleteme::Application
end

Now, the test will stop working. The functionality does work, as evidenced if you visit /so with your browser. It's only that the tests are not aware of that Rack setup.

Answer 1

(Thanks Dan Croak for setting me on the right track. This answer completes what he said).

Short answer

Can't be done for functional tests.

For integration tests, add the following to your test_helper.rb:

ActionDispatch::IntegrationTest.app = Rack::Builder.new do
  eval File.read(Rails.root.join('config.ru'))
end

Long answer

Functional tests are just unit tests run against controllers. When you say, for example get :index, you are not resolving a route. Instead, this is a shorthand for calling the index method, with a request environment that includes a mention to the HTTP method being GET.

Therefore, it makes sense that your Rack stack does not influence functional tests.

Integration tests are a different matter. You are testing your full stack there, so you will want to test your Rack middlewares too. Only problem is that, by default, these tests only see the middlewares that you add using Rails's own API.

But I say "by default" because Rails offers a way to change what Rack stack will be tested. By default, integration tests call Rails.application for their requests. You can change this to anything that suits your needs.

By using the code above, we use Rack::Builder create an ad-hoc Rack application. Inside the block, you can put any code that you would normally put inside a config.ru file. To avoid code duplication, eval loads our config.ru file. Now our integration tests will load exactly the same application that our app servers expose.

Answer 2

I think the problem is that ActionDispatch::IntegrationTest uses your Rails.application as its Rack app for the test.

So, if you can wrap that Rack::Rewrite rule into some Rack middleware, you should be able to override the Rack app you're testing in your test with:

ActionDispatch::IntegrationTest.app = MyRewriteMiddleware