Rename Feeds::ChangesetCommentsController to ChangesetComments::FeedsController

We usually create nested controllers with the main controller as the module,
and the nested controller as the specialization, e.g. Users::DeletionsController
or Traces::IconsController.

This then leaves the topic of whether the feed resource is plural, and whether we
are then showing a singular feed or showing a list (index) of objects.

The routes are carefully named so that we have `changesets_comments_feed_path` (the
comments feed for all changesets) vs `changeset_comment_feed_path(changeset)` (the
comments for a singular changeset).

test/controllers/changeset_comments/feeds_controller_test.rb

@@ -0,0 +1,72 @@
+require "test_helper"
+
+module ChangesetComments
+  class FeedsControllerTest < ActionDispatch::IntegrationTest
+    ##
+    # test all routes which lead to this controller
+    def test_routes
+      assert_routing(
+        { :path => "/changeset/1/comments/feed", :method => :get },
+        { :controller => "changeset_comments/feeds", :action => "show", :changeset_id => "1", :format => "rss" }
+      )
+      assert_routing(
+        { :path => "/history/comments/feed", :method => :get },
+        { :controller => "changeset_comments/feeds", :action => "show", :format => "rss" }
+      )
+    end
+
+    ##
+    # test comments feed
+    def test_feed
+      changeset = create(:changeset, :closed)
+      create_list(:changeset_comment, 3, :changeset => changeset)
+
+      get changesets_comments_feed_path(:format => "rss")
+      assert_response :success
+      assert_equal "application/rss+xml", @response.media_type
+      assert_select "rss", :count => 1 do
+        assert_select "channel", :count => 1 do
+          assert_select "item", :count => 3
+        end
+      end
+
+      get changesets_comments_feed_path(:format => "rss", :limit => 2)
+      assert_response :success
+      assert_equal "application/rss+xml", @response.media_type
+      assert_select "rss", :count => 1 do
+        assert_select "channel", :count => 1 do
+          assert_select "item", :count => 2
+        end
+      end
+
+      get changeset_comments_feed_path(changeset, :format => "rss")
+      assert_response :success
+      assert_equal "application/rss+xml", @response.media_type
+      last_comment_id = -1
+      assert_select "rss", :count => 1 do
+        assert_select "channel", :count => 1 do
+          assert_select "item", :count => 3 do |items|
+            items.each do |item|
+              assert_select item, "link", :count => 1 do |link|
+                match = assert_match(/^#{changeset_url changeset}#c(\d+)$/, link.text)
+                comment_id = match[1].to_i
+                assert_operator comment_id, "<", last_comment_id if last_comment_id != -1
+                last_comment_id = comment_id
+              end
+            end
+          end
+        end
+      end
+    end
+
+    ##
+    # test comments feed
+    def test_feed_bad_limit
+      get changesets_comments_feed_path(:format => "rss", :limit => 0)
+      assert_response :bad_request
+
+      get changesets_comments_feed_path(:format => "rss", :limit => 100001)
+      assert_response :bad_request
+    end
+  end
+end