title: Rack test error while using Capybara with Rails TestCase
body: <p>I've included Capybara in my integration tests. I've set up my test_helper file according to the documentation. </p>
  
  <pre><code>ENV['RAILS_ENV'] ||= 'test'
  require File.expand_path('../../config/environment', __FILE__)
  require 'rails/test_help'
  require 'capybara'
  require 'capybara/dsl'
  require 'vcr'
  
  class ActiveSupport::TestCase
    include Devise::Test::IntegrationHelpers
    # Setup all fixtures in test/fixtures/*.yml for all tests in alphabetical order.
    fixtures :all
  
    # Add more helper methods to be used by all tests here...
    VCR.configure do |c|
      c.hook_into :webmock
      c.cassette_library_dir = 'vcr_cassettes'
      c.default_cassette_options = { :record =&gt; :once }
    end
  end
  
  class ActionDispatch::IntegrationTest
    # Make the Capybara DSL available in all integration tests
    include Capybara::DSL
  
    # Reset sessions and driver between tests
    # Use super wherever this method is redefined in your individual test classes
    def teardown
      Capybara.reset_sessions!
      Capybara.use_default_driver
    end
  end
  </code></pre>
  
  <p>To test my integration test using Capybara, I set up a method in my portfolio_flow_test file (also require test_helper.rb)</p>
  
  <pre><code>test "signed in user can visit portfolio index page" do
    @user = users(:nicholas)
    sign_in @user
    visit portfolios_path
    assert_select "h1", "Portfolios"
  end
  </code></pre>
  
  <p>I get this error on all my tests</p>
  
  <pre><code>ArgumentError: rack-test requires a rack application, but none was given
  </code></pre>
  
  <p>Capybara's default driver is rack test so I'm unclear as to why it's failing when I'm running the tests.</p>