Refactor RSS view renderer

In issue #1815, it was reported that Gollum RSS feeds attempt to put
entire commit messages into a feed item's `<title>` element.

Given that commit messages can be many paragraphs long, this is not an
acceptable way to render a feed item title.

If a commit has many lines or paragraphs, we now put those inside the
`<description>` element as of this commit.

While I was editing this view, I decided it would be a good time to
increase test coverage, as this view renderer was not under test at
all. I also fixed a typo ("Commited" should say "Committed"). There are
implicit dependencies on other gems that provide the
`Gollum::Git::Commit`, `Gollum::Git::Actor`, and `Rugged::Commit`
classes here, so mocking out simple versions of their interfaces seemed
like the path of least resistance to setting up controllable tests.

I also removed some now-duplicated assertions from `test/test_app.rb`.

lib/gollum/views/rss.rb

@@ -1,43 +1,84 @@
 require 'rss'
 
 class RSSView
-  
   include Precious::Views::AppHelpers
   include Precious::Views::RouteHelpers
-  
+
   attr_reader :base_url
-  
+
   def initialize(base_url, wiki_title, url, changes)
     @base_url = base_url
     @wiki_title = wiki_title
     @url = url
     @changes = changes
   end
-  
+
   def render
-    latest_changes = "#{@url}#{latest_changes_path}"
     RSS::Maker.make('2.0') do |maker|
       maker.channel.author = 'Gollum Wiki'
-      maker.channel.updated = @changes.first.authored_date
-      maker.channel.title = "#{@wiki_title} Latest Changes"
       maker.channel.description = "Latest Changes in #{@wiki_title}"
-      maker.channel.link = latest_changes
+      maker.channel.link = latest_changes_url
+      maker.channel.title = "#{@wiki_title} Latest Changes"
+      maker.channel.updated = @changes.first.authored_date
+
       @changes.each do |change|
         maker.items.new_item do |item|
-          item.link = latest_changes
-          item.title = change.message
+          item.description = feed_item_description(change)
+          item.link = latest_changes_url
+          item.title = feed_item_title(change)
           item.updated = change.authored_date
-          id = change.id
-          files = change.stats.files.map do |files|
-            [files[:old_file], files[:new_file]].compact.map do |file|
-              f = extract_page_dir(file)
-              "<li><a href=\"#{@url}#{page_route(f)}/#{id}\">#{f}</a></li>"
-            end
-          end
-          item.description = "Commited by: <a href=\"mailto:#{change.author.email}\">#{change.author.name}</a><br/>Commit ID: #{id[0..6]}<br/><br/>Affected files:<ul>#{files.join}</ul>"
         end
       end
     end.to_s
   end
 
-end
+  private
+
+  def feed_item_commit_body(change)
+    body = change.message.lines[1..-1].join
+    body = body.split(/\n{2}/).map { |paragraph| "<p>#{paragraph}</p>" }.join
+    body.gsub!(/\n/, ' ')
+    body
+  end
+
+  def feed_item_description(change)
+    ERB.new(<<~HTML_PARTIAL)
+      <%= feed_item_commit_body(change) %>
+      Committed by: <a href="mailto:<%= change.author.email %>">
+        <%= change.author.name %>
+      </a><br />
+      Commit ID: <%= change.id[0..6] %><br /><br />
+      <%= feed_item_files(change) %>
+    HTML_PARTIAL
+      .result(binding)
+  end
+
+  def feed_item_files(change)
+    file_list = change.stats.files.map { |change_files|
+      [
+        change_files[:old_file],
+        change_files[:new_file]
+      ].compact
+    }
+
+    ERB.new(<<~HTML_PARTIAL)
+      Affected files: <ul>
+        <% file_list.each do |change_files| %>
+          <% change_files.each do |file| %>
+            <% file_href = "%s%s/%s" % [@url, page_route(file), change.id] %>
+            <li><a href="<%= file_href %>"><%= file %></a></li>
+          <% end %>
+        <% end %>
+      </ul>
+    HTML_PARTIAL
+      .result(binding)
+  end
+
+  def feed_item_title(change)
+    change.message.lines.first.strip
+  end
+
+  def latest_changes_url
+    "%s%s" % [@url, latest_changes_path]
+  end
+end