with_routing not working with get :index

As guys previously mentioned in the thread the problem is that `#get` is called on
other context then `#with_routing`.

It is caused by
https://github.com/rspec/rspec-rails/blob/master/lib/rspec/rails/example/controller_example_group.rb#L5.
ActionDispatch::Assertions::RoutingAssertions is adding #with_routing to
an assertion_instance, and ActionController::TestCase::Behavior is
adding #get to ControllerExampleGroup.

So I decided to add an ControllerAssertionDelegator which will include
both of them. Actually AssertionDelegator missed some methods, so I
featured them in that delegator.

Closes #1652

lib/rspec/rails/adapters.rb

@@ -112,6 +112,48 @@ def assertion_instance
       end
     end
 
+    # @private
+    class ControllerAssertionDelegator < AssertionDelegator
+      module Setup
+        extend ActiveSupport::Concern
+
+        included { init_setup }
+
+        module ClassMethods
+          attr_reader :setup_methods, :setup_blocks
+          attr_accessor :controller_class
+
+          def init_setup
+            @setup_methods ||= []
+            @setup_blocks ||= []
+          end
+
+          def setup(*methods, &block)
+            @setup_methods += methods
+            @setup_blocks << block if block
+          end
+        end
+
+        def initialize(*)
+          super
+          self.class.controller_class = described_class
+          run_setup
+        end
+
+        def run_setup
+          self.class.setup_methods.each { |m| send(m) }
+          self.class.setup_blocks.each { |b| b.call }
+        end
+      end
+
+      def initialize(*args)
+        args << Setup
+        args << ActionDispatch::Assertions::RoutingAssertions
+        args << ActionController::TestCase::Behavior
+        super(*args)
+      end
+    end
+
     # Adapts example groups for `Minitest::Test::LifecycleHooks`
     #
     # @private

lib/rspec/rails/example/controller_example_group.rb

@@ -1,9 +1,7 @@
 module RSpec
   module Rails
     # @private
-    ControllerAssertionDelegator = RSpec::Rails::AssertionDelegator.new(
-      ActionDispatch::Assertions::RoutingAssertions
-    )
+    ControllerAssertionDelegatorConst = RSpec::Rails::ControllerAssertionDelegator.new
 
     # @api public
     # Container module for controller spec functionality.
@@ -15,7 +13,7 @@ module ControllerExampleGroup
       include RSpec::Rails::Matchers::RedirectTo
       include RSpec::Rails::Matchers::RenderTemplate
       include RSpec::Rails::Matchers::RoutingMatchers
-      include ControllerAssertionDelegator
+      include ControllerAssertionDelegatorConst
 
       # Class-level DSL for controller specs.
       module ClassMethods