Check partial_rendered_times to clarify expectations.

It was difficult to see when the partials were rendered, and how many times
we expected it to be rendered before. Because we weren't explaining it.

actionpack/test/controller/caching_test.rb

@@ -417,8 +417,11 @@ def test_collection_fetches_cached_views
 
   def test_preserves_order_when_reading_from_cache_plus_rendering
     get :index, params: { id: 2 }
-    get :index_ordered
+    assert_equal 1, @controller.partial_rendered_times
+    assert_select ':root', 'david, 2'
 
+    get :index_ordered
+    assert_equal 3, @controller.partial_rendered_times
     assert_select ':root', "david, 1\n  david, 2\n  david, 3"
   end