Revert "Revert integration test refactoring that caused app test regressions"

This reverts commit 71420598.

actionpack/lib/action_dispatch/testing/integration.rb

@@ -388,8 +388,16 @@ module Runner
 
       APP_SESSIONS = {}
 
-      def app
-        @app ||= nil
+      attr_reader :app
+
+      def before_setup
+        super
+        @app = nil
+        @integration_session = nil
+      end
+
+      def integration_session
+        @integration_session ||= create_session(app)
       end
 
       # Reset the current session. This is useful for testing multiple sessions
@@ -417,8 +425,6 @@ def remove! # :nodoc:
       %w(get post patch put head delete cookies assigns
          xml_http_request xhr get_via_redirect post_via_redirect).each do |method|
         define_method(method) do |*args|
-          reset! unless integration_session
-
           # reset the html_document variable, except for cookies/assigns calls
           unless method == 'cookies' || method == 'assigns'
             @html_document = nil
@@ -450,19 +456,16 @@ def open_session
       # Copy the instance variables from the current session instance into the
       # test instance.
       def copy_session_variables! #:nodoc:
-        return unless integration_session
         @controller = @integration_session.controller
         @response   = @integration_session.response
         @request    = @integration_session.request
       end
 
       def default_url_options
-        reset! unless integration_session
         integration_session.default_url_options
       end
 
       def default_url_options=(options)
-        reset! unless integration_session
         integration_session.default_url_options = options
       end
 
@@ -472,7 +475,6 @@ def respond_to?(method, include_private = false)
 
       # Delegate unhandled messages to the current session instance.
       def method_missing(sym, *args, &block)
-        reset! unless integration_session
         if integration_session.respond_to?(sym)
           integration_session.__send__(sym, *args, &block).tap do
             copy_session_variables!
@@ -481,11 +483,6 @@ def method_missing(sym, *args, &block)
           super
         end
       end
-
-      private
-        def integration_session
-          @integration_session ||= nil
-        end
     end
   end
 
@@ -663,7 +660,6 @@ def app
     end
 
     def url_options
-      reset! unless integration_session
       integration_session.url_options
     end
 

actionpack/test/dispatch/response_test.rb

@@ -254,10 +254,6 @@ def test_response_body_encoding
 end
 
 class ResponseIntegrationTest < ActionDispatch::IntegrationTest
-  def app
-    @app
-  end
-
   test "response cache control from railsish app" do
     @app = lambda { |env|
       ActionDispatch::Response.new.tap { |resp|