Use a test setup similar to actiondispatch's Cookie Store tests

I took another look at the changes we had to make in #220 and compared
that to how things work in `actiondispatch`'s Cookie Store tests and
realized we were close, but missing how we were setting the options for
our store. So I've revamped the setup to be in line with what's in
Rails' own tests. This should make it easier to keep things in line and
working, going forward.

See the following two files for how Cookie Store tests (and their base
`ActionDispatch::IntegrationTest`) work today (as of Rails 8.0):
   * https://github.com/rails/rails/blob/8-0-stable/actionpack/test/dispatch/session/cookie_store_test.rb
   * https://github.com/rails/rails/blob/8-0-stable/actionpack/test/abstract_unit.rb

NOTE: The big downside to this is… it depends on some changes to how
`#with_routing`, provided by Rails, works. Meaning it only works with
Rails 7.2+. ☹️

Author: stevenharman

test/action_controller_test.rb

@@ -197,7 +197,9 @@ def test_prevents_session_fixation
   end
 
   def test_allows_session_fixation
-    with_test_route_set(:cookie_only => false) do
+    session_options(cookie_only: false)
+
+    with_test_route_set do
       get '/set_session_value'
       assert_response :success
       assert cookies['_session_id']
@@ -238,7 +240,9 @@ def test_incoming_invalid_session_id_via_cookie_should_be_ignored
   end
 
   def test_incoming_invalid_session_id_via_parameter_should_be_ignored
-    with_test_route_set(:cookie_only => false) do
+    session_options(cookie_only: false)
+
+    with_test_route_set do
       open_session do |sess|
         sess.get '/set_session_value', :params => { :_session_id => 'INVALID' }
         new_session_id = sess.cookies['_session_id']
@@ -252,7 +256,9 @@ def test_incoming_invalid_session_id_via_parameter_should_be_ignored
   end
 
   def test_session_store_with_all_domains
-    with_test_route_set(:domain => :all) do
+    session_options(domain: :all)
+
+    with_test_route_set do
       get '/set_session_value'
       assert_response :success
     end

test/helper.rb

@@ -44,7 +44,7 @@ def config
 class ActionDispatch::IntegrationTest < ActiveSupport::TestCase
   include ActionDispatch::SharedRoutes
 
-  def self.build_app(routes, options)
+  def self.build_app(routes = nil)
     RoutedRackApp.new(routes || ActionDispatch::Routing::RouteSet.new) do |middleware|
       middleware.use ActionDispatch::DebugExceptions
       middleware.use ActionDispatch::ActionableExceptions
@@ -53,16 +53,25 @@ def self.build_app(routes, options)
       middleware.use ActionDispatch::Flash
       middleware.use Rack::MethodOverride
       middleware.use Rack::Head
-      middleware.use ActionDispatch::Session::ActiveRecordStore, options.reverse_merge(key: "_session_id")
       yield(middleware) if block_given?
     end
   end
 
-  self.app = build_app(nil, {})
+  self.app = build_app
 
   private
 
-    def with_test_route_set(options = {})
+    def session_options(options = {})
+      (@session_options ||= {key: "_session_id"}).merge!(options)
+    end
+
+    def app
+      @app ||= self.class.build_app do |middleware|
+        middleware.use ActionDispatch::Session::ActiveRecordStore, session_options
+      end
+    end
+
+    def with_test_route_set
       controller_namespace = self.class.to_s.underscore
       actions = %w[set_session_value get_session_value call_reset_session renew get_session_id]
 
@@ -71,14 +80,7 @@ def with_test_route_set(options = {})
           actions.each { |action| get action, controller: "#{controller_namespace}/test" }
         end
 
-        old_app = self.class.app
-        begin
-          self.class.app = self.class.build_app(set, options)
-
-          yield
-        ensure
-          self.class.app = old_app
-        end
+        yield
       end
     end