rack_test_hack.rb

# Rack::Test doesn't support hitting external webservers.  However, when a user enters their credit card info,
# it is submitted directly to braintree, so we need to intregration test with hitting an external server.

# This hack enabled this, by swapping out the Rack::Test's rack app with a Rack::Client instance.
# Rack::Client acts just like a rack app, but under the covers it delegates to Net::HTTP.

require 'rack/client'

module RackTestHack
  def new(*a, &b)
    super.extend Extension
  end

  module Extension
    def __remote_host?(uri)
      # ignore subdomains...
      uri_domain = uri.host.split('.')[-2, 2]
      default_domain = default_host.split('.')[-2, 2]
      uri_domain != default_domain && uri_domain.first != 'example'
    end

    def __fix_env(uri, env)
      # Braintree depends on the query string being in an exact order, but rack-test rearranges the query string a bit.
      # So, we fix it here by re-setting the query string if the params are the ones needed by braintree.
      if Rack::Request.new(env).params.keys.sort == %w( hash http_status id )
        env['QUERY_STRING'] = uri.query
      end
    end

    def request(uri, env)
      orig_app = @app
      @app = Rack::Client.new if __remote_host?(uri)
      __fix_env(uri, env)
      begin
        super
      ensure
        @app = orig_app
      end
    end
  end
end

Rack::MockSession.extend RackTestHack

I think __remote_host? method needs to check for localhost

def __remote_host?(uri)
return false if uri.host=="localhost"
uri_domain = uri.host.split('.')[-2, 2]
default_domain = default_host.split('.')[-2, 2]
uri_domain != default_domain && uri_domain.first != 'example'
end

Myron, thanks for sharing this! Have you found more clean solution since then?