Make IntegrationTest::Runner propagate method_missing to ancestors.

Fixes RSpec integration example groups, which mixes its Matchers
module into ActiveSupport::TestCase.
Signed-off-by: NMichael Koziarski <michael@koziarski.com>

actionpack/lib/action_dispatch/testing/integration.rb

@@ -396,8 +396,12 @@ def copy_session_variables! #:nodoc:
       # Delegate unhandled messages to the current session instance.
       def method_missing(sym, *args, &block)
         reset! unless @integration_session
-        returning @integration_session.__send__(sym, *args, &block) do
-          copy_session_variables!
+        if @integration_session.respond_to?(sym)
+          returning @integration_session.__send__(sym, *args, &block) do
+            copy_session_variables!
+          end
+        else
+          super
         end
       end
     end

actionpack/test/controller/integration_test.rb

@@ -199,6 +199,24 @@ def test_opens_new_session
     assert_equal ::ActionController::Integration::Session, session2.class
     assert_not_equal session1, session2
   end
+
+  # RSpec mixes Matchers (which has a #method_missing) into
+  # IntegrationTest's superclass.  Make sure IntegrationTest does not
+  # try to delegate these methods to the session object.
+  def test_does_not_prevent_method_missing_passing_up_to_ancestors
+    mixin = Module.new do
+      def method_missing(name, *args)
+        name.to_s == 'foo' ? 'pass' : super
+      end
+    end
+    @test.class.superclass.__send__(:include, mixin)
+    begin
+      assert_equal 'pass', @test.foo
+    ensure
+      # leave other tests as unaffected as possible
+      mixin.__send__(:remove_method, :method_missing)
+    end
+  end
 end
 
 # Tests that integration tests don't call Controller test methods for processing.