diff --git a/actionpack/lib/action_controller/metal/renderers.rb b/actionpack/lib/action_controller/metal/renderers.rb
index 1f77f9ecaa..f171c4d172 100644
--- a/actionpack/lib/action_controller/metal/renderers.rb
+++ b/actionpack/lib/action_controller/metal/renderers.rb
@@ -11,6 +11,7 @@ module ActionController
     Renderers.remove(key)
   end
 
+  # See <tt>Responder#api_behavior</tt>
   class MissingRenderer < LoadError
     def initialize(format)
       super "No renderer defined for format: #{format}"
@@ -67,6 +68,11 @@ module ActionController
       alias use_renderer use_renderers
     end
 
+    # Called by +render+ in <tt>AbstractController::Renderering</tt>
+    # which sets the return value as the +response_body+.
+    #
+    # If no renderer is found, +super+ returns control to
+    # <tt>ActionView::Rendering.render_to_body</tt>, if present.
     def render_to_body(options)
       _render_to_body_with_renderer(options) || super
     end
@@ -137,6 +143,9 @@ module ActionController
       remove_method(method_name) if method_defined?(method_name)
     end
 
+    # Used in <tt>ActionController::Base</tt>
+    # and <tt>ActionController::API</tt> to include all
+    # renderers by default.
     module All
       extend ActiveSupport::Concern
       include Renderers
diff --git a/actionpack/test/controller/render_other_test.rb b/actionpack/test/controller/render_other_test.rb
deleted file mode 100644
index 1f5215ac55..0000000000
--- a/actionpack/test/controller/render_other_test.rb
+++ /dev/null
@@ -1,24 +0,0 @@
-require 'abstract_unit'
-
-
-class RenderOtherTest < ActionController::TestCase
-  class TestController < ActionController::Base
-    def render_simon_says
-      render :simon => "foo"
-    end
-  end
-
-  tests TestController
-
-  def test_using_custom_render_option
-    ActionController.add_renderer :simon do |says, options|
-      self.content_type  = Mime[:text]
-      self.response_body = "Simon says: #{says}"
-    end
-
-    get :render_simon_says
-    assert_equal "Simon says: foo", @response.body
-  ensure
-    ActionController.remove_renderer :simon
-  end
-end
diff --git a/actionpack/test/controller/renderers_test.rb b/actionpack/test/controller/renderers_test.rb
new file mode 100644
index 0000000000..e6c2e4636e
--- /dev/null
+++ b/actionpack/test/controller/renderers_test.rb
@@ -0,0 +1,90 @@
+require 'abstract_unit'
+require 'controller/fake_models'
+require 'active_support/logger'
+
+class RenderersTest < ActionController::TestCase
+  class XmlRenderable
+    def to_xml(options)
+      options[:root] ||= "i-am-xml"
+      "<#{options[:root]}/>"
+    end
+  end
+  class JsonRenderable
+    def as_json(options={})
+      hash = { :a => :b, :c => :d, :e => :f }
+      hash.except!(*options[:except]) if options[:except]
+      hash
+    end
+
+    def to_json(options = {})
+      super :except => [:c, :e]
+    end
+  end
+  class CsvRenderable
+    def to_csv
+      "c,s,v"
+    end
+  end
+  class TestController < ActionController::Base
+
+    def render_simon_says
+      render :simon => "foo"
+    end
+
+    def respond_to_mime
+      respond_to do |type|
+        type.json do
+          render json: JsonRenderable.new
+        end
+        type.js   { render json: 'JS', callback: 'alert' }
+        type.csv  { render csv: CsvRenderable.new    }
+        type.xml  { render xml: XmlRenderable.new     }
+        type.html { render body: "HTML"    }
+        type.rss  { render body: "RSS"     }
+        type.all  { render body: "Nothing" }
+        type.any(:js, :xml) { render body: "Either JS or XML" }
+      end
+    end
+  end
+
+  tests TestController
+
+  def setup
+    # enable a logger so that (e.g.) the benchmarking stuff runs, so we can get
+    # a more accurate simulation of what happens in "real life".
+    super
+    @controller.logger = ActiveSupport::Logger.new(nil)
+  end
+
+  def test_using_custom_render_option
+    ActionController.add_renderer :simon do |says, options|
+      self.content_type  = Mime[:text]
+      self.response_body = "Simon says: #{says}"
+    end
+
+    get :render_simon_says
+    assert_equal "Simon says: foo", @response.body
+  ensure
+    ActionController.remove_renderer :simon
+  end
+
+  def test_raises_missing_template_no_renderer
+    assert_raise ActionView::MissingTemplate do
+      get :respond_to_mime, format: 'csv'
+    end
+    assert_equal Mime[:csv], @response.content_type
+    assert_equal "", @response.body
+  end
+
+  def test_adding_csv_rendering_via_renderers_add
+    ActionController::Renderers.add :csv do |value, options|
+      send_data value.to_csv, type: Mime[:csv]
+    end
+    @request.accept = "text/csv"
+    get :respond_to_mime, format: 'csv'
+    assert_equal Mime[:csv], @response.content_type
+    assert_equal "c,s,v", @response.body
+  ensure
+    ActionController::Renderers.remove :csv
+  end
+end