diff --git a/actionpack/lib/action_controller/integration.rb b/actionpack/lib/action_controller/integration.rb
index d9899112c37fa32ef9dda98e3c5ce90610ae9681..ded72a71fb887c586aae357e365d3cf9c04a6b9a 100644
--- a/actionpack/lib/action_controller/integration.rb
+++ b/actionpack/lib/action_controller/integration.rb
@@ -367,8 +367,10 @@ def process(method, path, parameters = nil, headers = nil)
             env[key] = value
           end
 
-          unless ActionController::Base.respond_to?(:clear_last_instantiation!)
-            ActionController::Base.module_eval { include ControllerCapture }
+          [ControllerCapture, ActionController::ProcessWithTest].each do |mod|
+            unless ActionController::Base < mod
+              ActionController::Base.class_eval { include mod }
+            end
           end
 
           ActionController::Base.clear_last_instantiation!
@@ -396,6 +398,7 @@ def process(method, path, parameters = nil, headers = nil)
           if @controller = ActionController::Base.last_instantiation
             @request = @controller.request
             @response = @controller.response
+            @controller.send(:set_test_assigns)
           else
             # Decorate responses from Rack Middleware and Rails Metal
             # as an Response for the purposes of integration testing